WARNING SYSTEM

Warning Lights

The Master Caution system was developed for the 737 to ease pilot workload as it was the first Boeing airliner to be produced without a flight engineer. In simple terms it is an attention getter that also directs the pilot toward the problem area concerned. The system annunciators (shown above) are arranged such that the cautions are in the same orientation as the overhead panel e.g. FUEL bottom left, DOORS bottom of third column, etc.
On the ground, the master caution system will also tell you if the condition is dispatchable or if the QRH needs to be actioned. The FCOM gives the following guidance on master caution illuminations on the ground:

Before engine start, use individual system lights to verify the system status. If an individual system light indicates an improper condition:
• check the Dispatch Deviations Procedures Guide (DDPG) or the operator equivalent to decide if the condition has a dispatch effect
• decide if maintenance is needed
If, during or after engine start, a red warning or amber caution light illuminates:
• do the respective non-normal checklist (NNC)
• on the ground, check the DDPG or the operator equivalent
If, during recall, an amber caution illuminates and then extinguishes after a master caution reset:
• check the DDPG or the operator equivalent
• the respective non-normal checklist is not needed

Pressing the system annunciator will show any previously cancelled or single channel cautions. If a single channel caution is encountered, the QRH drill should not be actioned.
Master caution lights and the system annunciator are powered from the battery bus and will illuminate when an amber caution light illuminates. Exceptions to this include a single centre fuel tank LOW PRESSURE light (requires both), REVERSER lights (requires 12 seconds) and INSTR SWITCH (inside normal FoV).
When conducting a light test, during which the system will be inhibited, both bulbs of each caution light should be carefully checked. The caution lights are keyed to prevent them from being replaced incorrectly, but may be interchanged with others of the same caption

Technical Specifications NG

Technical Specifications classic

Technical Specifications Original

ACCIDENT

PRODUCTION

PRODUCTION

RUDDER SYSTEM

By Derek Watts & Chris Brady

For the background to the rudder history click here.

Yaw control is achieved by a single graphite / composite rudder panel. A single rudder power control unit (PCU) controls rudder panel deflection. A standby rudder PCU provides back up in the event of malfunction of the main rudder PCU. There is no manual reversion for yaw control. The only internal indication of rudder panel deflection is pedal position, which always accurately reflects control surface deflection. Total authority of the control surface is modulated in relation to aircraft IAS using “blowdown”, ie a constant pressure is applied to the surface by the actuator, and the movement of the panel reduces accordingly as the dynamic pressure on it increases. For this reason maximum rudder pedal movement is reduced with increasing airspeed. Maximum rudder panel deflection is approximately +/-15 degrees on the ground, reducing to around +/-8 degrees at a typical cruise altitude

(PCU)Power Control Unit

The rudder PCU consists of an input shaft / crank mechanism, a dual concentric servo valve to control porting of the fluid to the rudder actuator, and a yaw damper actuator. The rudder actuator is a tandem actuator, having two internal piston areas for each hydraulic source (A & B). The actuator is capable of positioning the rudder panel with either one or both main hydraulic sources available, though with one source inoperative a reduced rudder panel deflection would result due to blowdown at higher airspeeds.
Flow of hydraulic fluid to the rudder actuator is controlled by the dual servo-valve. This is a complex dual concentric cylinder with an outer and inner slide. During normal rudder pedal inputs sufficient rudder panel deflection is catered for by the primary (inner) valve alone. However, should a larger panel deflection be required or a higher rate rudder input be commanded, the secondary (outer) sleeve moves in addition to port extra fluid to the actuator. Movement of the outer sleeve is typically no more than 1mm. Position of both sleeves of the servo valve is controlled by a complex mechanism of bell cranks, input rod and summing lever, the geometry of which is such as to provide movement of the sleeves in relation to the body of the valve.
The 737NG also has a standby rudder PCU that moves the rudder during manual reversion operation. The wheel-torudder interconnect system (WTRIS) will coordinate (assist) turns by using the standby rudder PCU to apply rudder as necessary based upon the Captains control wheel roll inputs. From experience, I can verify that this makes the NG much easier to handle in manual reversion than previous generations

Yaw Damper

The yaw damper is incorporated to prevent Dutch roll. It is connected in parallel with the main servo valve and includes its own actuator, powered by hydraulic system B. This actuator applies its own input to the input shaft / crank mechanism to bring about a movement of the servo-valve and hence a rudder panel deflection. No pedal movement results from yaw damper operation. Total authority of the yaw damper is approximately +/-2.5 degrees.
NGs: The 737-NGs also have a standby yaw damper; it uses the standby rudder PCU, with commands from SMYD 2 and powered by the standby hydraulic system. SMYD 1 controls the main yaw damper with hydraulic system B. Note: Only inputs from the main yaw damper are shown on the yaw damper indicator.
 

Rudder Pressure Reducer (RPR) - 3/4/500

To limit the effects of various PCU failure modes (pre-RSEP), a rudder pressure reducer (RPR) was fitted to the Asystem pressure side of the rudder PCU. This is simply a pressure reducing valve, which operates during the majority of flight phases to reduce the total authority of the rudder panel by approximately one-third. The B-system portion of the rudder PCU is unaffected by the RPR, as is yaw damper operation

During certain critical phases of flight when full rudder authority may be required, the RPR provides full system pressure (3000psi from 1800psi) to the rudder PCU. These are: - 

a)     During take-off below 1000’ Rad.alt.

b)     During approach below 700’ Rad.alt.

c)      If a difference of >45% N1 exists between power units.

d)     If B-system hydraulic pressure is lost.

Whilst correct functioning of the RPR is transparent to the flight crew, certain cockpit indications can be helpful in verifying correct operation and faults alike; the A system flight controls low pressure warning light now has two additional functions related purely to the RPR; on initial application of pressure to hydraulic system A, the lowpressure warning light should remain illuminated for 5 seconds. If the light extinguishes immediately then a fault may be present within the RPR. Incorrect mode switching of the RPR is also indicated by illumination of the light on approach below 700ft RA, indicating that full pressure is not available to the A-system portion of the rudder PCU. A further associated failure of hydraulic system B and an asymmetric thrust condition may result in insufficient rudder authority to maintain directional control.

Digital Yaw Damper Coupler

The yaw damper coupler comprises the control electronics and yaw rate gyro. A digital yaw damper coupler helps reduce the possibility of electro-magnetic interference (EMI). Turn co-ordination is provided by reducing the gain of the yaw-rate gyro in proportion to bank angle detected from the IRU. In this way during a turn the yaw damper coupler is “tricked” into believing the aircraft is yawing into the turn and provides an increased rudder input. The coupler is sensitive only to yaw rates that produce Dutch Roll. Note that the yaw damper coupler controls and monitors both the RPR (Sys A) and RPL (Sys B) of the main rudder PCU, a de-activated yaw damper also renders the RPR & RPL inoperative. For this reason higher block manoeuvring speeds are used when the yaw damper is u/s (not NGs).

Rudder System Enhancement Program (RSEP)

The Rudder System Enhancement Program (RSEP) introduced in 2003 (SB 737-27-1252/3/5) must be implemented on all series of 737s by 12 Nov 2008. It replaces the infamous dual concentric servo valve with separate input rods, control valves and actuators; one set for hydraulic system A, and one set for hydraulic system B. The standby PCU is controlled by a separate input rod and control valve powered by the standby hydraulic system. All three input rods have individual jam override mechanisms that allow inputs to be transferred to the remaining free rods if a jam occurs. All 737s must be fitted with the RSEP by Nov 2008. Modified aircraft are identifiable by the STBY RUD ON light on the flight controls panel and new c/bs on the P6-2 panel labelled “Force Fight Monitor” (all series) and “Rudder Load Limiter” (not NGs).

Force Fight Monitor (FFM)

The main rudder PCU contains a Force Fight Monitor (FFM) that detects opposing pressure (force fight) between A & B actuators, this may happen if either hydraulic system, input rod or control valve has jammed or failed. If this condition is detected for more than 5 seconds, the FFM will automatically turn on the standby hydraulic pump pressurising the standby rudder PCU. This will also illuminate the new STBY RUD ON light on the flight control panel

Lights

From L to R along the panel:

O/B Landing: (Not NG) Three position switch Off - Extend (off) - On. These are located on the outboard flap faring. 

Retractable Landing: (NG only) Replaces the outboard landing lights on the earlier series. These are located on the fuselage just beneath the ram air intakes. The word is that they may be being moved back to their original position on the flap track faring due to excessive stone damage.

Note Use of both of these lights should be avoided at speeds above 250kts due to excessive air loads on their hinges

I/B Landing: Known as fixed landing lights on the NG. Are located in the wing roots, usually used for all day and night landings for conspicuity.

R/W Turnoff: Also in the wing roots, normally only used at night on poorly lit runways.

Taxi: This 250W light is located on the nose gear, on later models it will switch off automatically with gear retraction. It is common practice to have this on whilst the aircraft is in motion as a warning to other aircraft and vehicles.

Logo: Are on each wingtip or horizontal stabiliser and illuminate the fin. Apart from the advertising value on the ground, they are often used for conspicuity in busy airspace.

Position: Depending upon customer option this can be a three position switch (as illustrated) to combine the strobe. Strobe & Steady / Off / Steady, where steady denotes the red, green & white navigation lights. The three Nav lights are no-go items at night.

Strobe: (Not illustrated) Off / Auto / On. Auto is activated by a squat switch. They are also in the wing tips and are very brilliant. This gives rise to great debate amongst pilots about when exactly they should be switched on as they can dazzle other pilots nearby. many people choose to put them on as they enter an active runway for conspicuity against landing traffic.

Anti-Collision: Are the orange rotating beacons above and below the fuselage. They are universally used as a signal that the engines are running or are about to be started. They are typically not switched off until N1 has reduced to below 3.5% (or N2 below 20%) when it is considered safe for ground personnel to approach the aircraft.

Wing: These are mounted in the fuselage and shine down the leading edge of the wing for ice or damage inspection at night.

Wheel Well: Illuminates the main and nose wheel wells. Normally only used during the turnaround at night for the pre-flight inspection but must also be on to see through the gear downlock viewers at night, hence they are a no-go item at night in all but the NG's. There is also a switch for the main wheel well light in the port wheel well.

Water System

There is a 30 US Gal tank (40 US Gal –400 series) behind the aft cargo hold for potable water. This serves the galleys and washbasins, but not the toilets as they use chemicals. Waste water is either drained into the toilet tanks or expelled through heated drain masts.

The tank indicator (-3/4/500 version shown left) is located over the rear service door. Press to test, indications are clockwise from 7 O'clock: Empty, 1/4, 1/2, 3/4, Full. The NG has an LED panel that is always lit (below) for both potable water and waste tank

AIRCRAFT FUSELAGE

EYEBROW WINDOWS

On the 3rd Feb 2005, 737-700, N201LV, L/N 1650, was the first ever 737 to fly without eyebrow windows (window numbers 4 & 5). They have been standard in Boeing aircraft back as far as WW2 bombers to give better crew visibility. Now they have been declared obsolete and removed from production. The design change reduces airplane weight by 20 pounds and eliminates approximately 300 hours of periodic inspections per airplane. Retrofit kits to cover eyebrow windows will be available mid-2006 for the in-service 737 fleet.
Note the windows will still be available as a customer option and all military versions will continue to be delivered with eyebrow windows.
Notice the 10 small vortex generators above the radome. These reduce the cockpit noise from the windshield by 3dB

LAP JOINTS

After the Aloha 737-200 accident, in which a 12ft x 8ft section of the upper fuselage tore away in flight, all 737's with over 50,000 cycles must have their lap joints reinforced with external doublers. This tired old aircraft is a 737-200 and the patching is clearly visable. This modification takes about 15,000 man hours and unfortunately has sometimes been the source of another problem - scoring. This is when metal instruments instead of wooden ones have been used to scrape away excess sealant or old paint from the lap joints which create deep scratches which may themselves develop into cracks.

5 May 2004 - Defects In Aging Passenger Jets Exposed
SEATTLE -- KIRO Team 7 Investigators discover cracks, corrosion and weakened metal hidden inside a growing number of Boeing passenger jets.
The problems lie along structural seams called lap joints. A fuselage is designed with overlapping sheets of metal riveted together. We uncovered at least 28 different warnings regarding flaws or defects. In 2002, a China Airlines jet plummeted into the water, killing 225 passengers. Fourteen years earlier, an Aloha Airlines 737 opened up like a sardine can, killing one person and injuring eight more.
KIRO 7 Eyewitness News Investigative Reporter Chris Halsne discovers a big new problem for Boeing, centered on "lap-joint metal fatigue". The problem is called "scoring". During assembly, workers lay a bead of sealant along this lap joint. It makes the jet more aerodynamic. A year or two flying you around and many jets have to get repainted. Powerful chemical strippers melt the sealant, so some maintenance crews have been putting on caulk then, according to the Federal Aviation Administration, have been cutting away the excess with a box cutter. That can ruin the integrity of the metal along the entire aircraft lap joint. The FAA recently grounded three passenger jets due to "scribe marks" and has identified 32 more Boeing planes with damaging box cutter-type cuts along the lap joint. "When we found this, we jumped on it right away," said FAA spokesperson Mike Fergus. Fergus says they have no idea yet how many more jets are affected by scoring. "With the contraction and expansion of thousands of flight hours, the scratch has the potential, not a guarantee, the potential of turning into a crack. That in turn may have safety factor. That's our issue. If it's safety, we're interested," Fergus said.
Scoring of some lap joints is just the latest chapter in Boeing's long battle with the design and maintenance of its riveted seams. "With that type of structure, whatever is occurring between the two sheets is not readily visible," said Earl Brown, a certified jet engine and airframe mechanic. Brown says the FAA has been warning airlines to inspect -- and re-inspect often -- the lap joints of thousands of still-operating older model Boeing jets. "If we can catch a problem when it's still just a crack and fix it, then we don't have to worry about something coming apart, breaking. The potential for breaking is there if a crack develops. It's pretty much inherent in the design of the airplane and the materials used," Brown said. The scoring issue has been kept quiet until now, but other huge maintenance nightmares include hundreds of previously "patched" or repaired planes.
An Airworthiness Directive says new inspections are necessary to find "premature cracking of certain lap joints, which could result in rapid decompression." Spotting fatigue in the lap joints on the outside of an aircraft, through the paint, is nearly impossible. So here's what the airlines have to do: They have to bring the jet into a hanger and gut the interior. That can cost more than $1 million.
The super-high cost of that "D-check" inspection is hardly an incentive for airlines to look really hard for trouble spots. For example, KIRO Team 7 Investigators uncovered an Aviation Safety Report filed by a mechanic last year. He reported his company ignored a potentially deadly safety problem saying, "A B737-200 had water leaking on passengers and inspectors found all fuselage lap joints leaking excessively." Despite that, the mechanic says the supervisor "told me to get off the ACFT and not to check any laps. This ACFT had to go."
Independent aviation robotics engineer Henry Seemann doesn't look at a Boeing 737 like the rest of us. We view them as a whole. He sees them in tiny parts, up close, one rivet at a time. And what he sees should make all of us a little nervous: cascading metal cracks, loose shear clips, corroded lap joints and tiny cuts in the metal. Halsne: "Are there times when you walk up to a plane and think, 'I don't know about this one?'" Seemann: "Yes, I've had my moments of certain airplanes when I've looked at them and actually booked a different flight." Seemann invented a machine, currently used by Boeing itself, that automatically inspects lap joints. The robot could save the industry billions in early maintenance because it takes just a few days to computer map and analyze lap joint flaws. Current methods take a month.
Despite the potential cost savings some airlines are telling Henry don't get that thing near our passenger jets. "There's a requirement that if you know something is wrong with your airplane, you're supposed to fix it. It's a moral thing," Seemann said. "Some are afraid of that -- that their fleet is kind of old and we're going to inspect their planes and we're going to put a big red "x" on them." The Federal Aviation Administration confirms this robot design is in the final stages of approval. It could revolutionize the way we spot catastrophic metal failures - before a serious accident.
Boeing refused our repeated requests for an on-camera interview about "scoring" and other lap joint issues, but did provide us with some background on how it's working hard to fix the problems. We called Boeing again this week for a statement. While they still won't comment on past metal fatigue issues, they did say design improvements on their new line of 7E7's should take care of future problems

RADOME

The radome (RAdar DOME) is an aerodynamic faring that houses the weather radar and ILS localiser and glideslope antennas. Unlike the rest of the fuselage it is made of fibreglass to allow the RF signals through.
Fibreglass is non-conductive which would allow the build up of P-static (static due to the motion of the aircraft through precipitation). This would in turn cause static interference on the antenna within so the radome is fitted with six conductive diverter strips on the outside to dissipate P-static into the airframe.

AFT BODY VORTEX GENERATORS


There are four vortex generators on each side of the rear fuselage above the horizontal stabiliser. The 737-1/200s also had three vortex generators below each stabiliser. They were probably installed to energise the airflow at the stagnation point at the tailcone, thereby reducing drag and giving a slight performance advantage.
Classics were initially produced without any aft body vortex generators (see photo. However the upper vortex generators were reinstated after line number 2277 (May 1992 onwards). This was to reduce elevator and elevator tab vibration during flight to increase their hinge bearing service life.
The CDL says that if any of these vortex generators are not fitted or missing “occasional vertical motions may be felt which appear to be light turbulence These motions are characteristic of this airplane and should not be construed to be associated with Mach buffet.”

technical Description of rudder

RUDDER SYSTEM

Yaw control is achieved by a single graphite / composite rudder panel. A single rudder power control unit (PCU) controls rudder panel deflection. A standby rudder PCU provides back up in the event of malfunction of the main rudder PCU. There is no manual reversion for yaw control. The only internal indication of rudder panel deflection is pedal position, which always accurately reflects control surface deflection. Total authority of the control surface is modulated in relation to aircraft IAS using “blowdown”, ie a constant pressure is applied to the surface by the actuator, and the movement of the panel reduces accordingly as the dynamic pressure on it increases. For this reason maximum rudder pedal movement is reduced with increasing airspeed. Maximum rudder panel deflection is approximately +/-15 degrees on the ground, reducing to around +/-8 degrees at a typical cruise altitude.


Power Control Unit (PCU)

The rudder PCU consists of an input shaft / crank mechanism, a dual concentric servo valve to control porting of the fluid to the rudder actuator, and a yaw damper actuator. The rudder actuator is a tandem actuator, having two internal piston areas for each hydraulic source (A & B). The actuator is capable of positioning the rudder panel with either one or both main hydraulic sources available, though with one source inoperative a reduced rudder panel deflection would result due to blowdown at higher airspeeds.
Flow of hydraulic fluid to the rudder actuator is controlled by the dual servo-valve. This is a complex dual concentric cylinder with an outer and inner slide. During normal rudder pedal inputs sufficient rudder panel deflection is catered for by the primary (inner) valve alone. However, should a larger panel deflection be required or a higher rate rudder input be commanded, the secondary (outer) sleeve moves in addition to port extra fluid to the actuator. Movement of the outer sleeve is typically no more than 1mm. Position of both sleeves of the servo valve is controlled by a complex mechanism of bell cranks, input rod and summing lever, the geometry of which is such as to provide movement of the sleeves in relation to the body of the valve.
The 737NG also has a standby rudder PCU that moves the rudder during manual reversion operation. The wheel-torudder interconnect system (WTRIS) will coordinate (assist) turns by using the standby rudder PCU to apply rudder as necessary based upon the Captains control wheel roll inputs. From experience, I can verify that this makes the NG much easier to handle in manual reversion than previous generations.
 
 

YAW DAMPER


The yaw damper is incorporated to prevent Dutch roll. It is connected in parallel with the main servo valve and includes its own actuator, powered by hydraulic system B. This actuator applies its own input to the input shaft / crank mechanism to bring about a movement of the servo-valve and hence a rudder panel deflection. No pedal movement results from yaw damper operation. Total authority of the yaw damper is approximately +/-2.5 degrees.
NGs: The 737-NGs also have a standby yaw damper; it uses the standby rudder PCU, with commands from SMYD 2 and powered by the standby hydraulic system. SMYD 1 controls the main yaw damper with hydraulic system B. Note: Only inputs from the main yaw damper are shown on the yaw damper indicator.

 

Rudder Pressure Reducer (RPR) - 3/4/500

To limit the effects of various PCU failure modes (pre-RSEP), a rudder pressure reducer (RPR) was fitted to the Asystem pressure side of the rudder PCU. This is simply a pressure reducing valve, which operates during the majority of flight phases to reduce the total authority of the rudder panel by approximately one-third. The B-system portion of the rudder PCU is unaffected by the RPR, as is yaw damper operation

During certain critical phases of flight when full rudder authority may be required, the RPR provides full system pressure (3000psi from 1800psi) to the rudder PCU. These are: - 

a)     During take-off below 1000’ Rad.alt.

b)     During approach below 700’ Rad.alt.

c)      If a difference of >45% N1 exists between power units.

d)     If B-system hydraulic pressure is lost.

Whilst correct functioning of the RPR is transparent to the flight crew, certain cockpit indications can be helpful in verifying correct operation and faults alike; the A system flight controls low pressure warning light now has two additional functions related purely to the RPR; on initial application of pressure to hydraulic system A, the lowpressure warning light should remain illuminated for 5 seconds. If the light extinguishes immediately then a fault may be present within the RPR. Incorrect mode switching of the RPR is also indicated by illumination of the light on approach below 700ft RA, indicating that full pressure is not available to the A-system portion of the rudder PCU. A further associated failure of hydraulic system B and an asymmetric thrust condition may result in insufficient rudder authority to maintain directional control

Digital Yaw Damper Coupler

The yaw damper coupler comprises the control electronics and yaw rate gyro. A digital yaw damper coupler helps reduce the possibility of electro-magnetic interference (EMI). Turn co-ordination is provided by reducing the gain of the yaw-rate gyro in proportion to bank angle detected from the IRU. In this way during a turn the yaw damper coupler is “tricked” into believing the aircraft is yawing into the turn and provides an increased rudder input. The coupler is sensitive only to yaw rates that produce Dutch Roll. Note that the yaw damper coupler controls and monitors both the RPR (Sys A) and RPL (Sys B) of the main rudder PCU, a de-activated yaw damper also renders the RPR & RPL inoperative. For this reason higher block manoeuvring speeds are used when the yaw damper is u/s (not NGs).

Rudder System Enhancement Program (RSEP)

The Rudder System Enhancement Program (RSEP) introduced in 2003 (SB 737-27-1252/3/5) must be implemented on all series of 737s by 12 Nov 2008. It replaces the infamous dual concentric servo valve with separate input rods, control valves and actuators; one set for hydraulic system A, and one set for hydraulic system B. The standby PCU is controlled by a separate input rod and control valve powered by the standby hydraulic system. All three input rods have individual jam override mechanisms that allow inputs to be transferred to the remaining free rods if a jam occurs. All 737s must be fitted with the RSEP by Nov 2008. Modified aircraft are identifiable by the STBY RUD ON light on the flight controls panel and new c/bs on the P6-2 panel labelled “Force Fight Monitor” (all series) and “Rudder Load Limiter” (not NGs).

Force Fight Monitor (FFM)

The main rudder PCU contains a Force Fight Monitor (FFM) that detects opposing pressure (force fight) between A & B actuators, this may happen if either hydraulic system, input rod or control valve has jammed or failed. If this condition is detected for more than 5 seconds, the FFM will automatically turn on the standby hydraulic pump pressurising the standby rudder PCU. This will also illuminate the new STBY RUD ON light on the flight control panel

Rudder Pressure Limiter (Not NGs)

This is effectively the B system equivalent of the RPR, except that it is physically part of the main rudder PCU rather than upstream of it. Hydraulic system B pressure is reduced within the main PCU from 3000 to 2200psi it has the same activation criteria as the RPR

NGs

The NGs do not have an RPR or RPL, but two Load Limiters instead (Shown as “CONTROL VALVE”s in the FCOM schematics). At speeds above approximately 135kts, hydraulic system A pressure (Pre-RSEP), hydraulic system A and B pressure (Post-RSEP) to the rudder PCU is reduced to 1450psi (Pre-RSEP) / 2200psi (Post-RSEP). They both reduce rudder output force by 25% at blowdown speed. The NGs also gained the FFM and separate input rods, control valves and actuators of the RSEP package.

Analysis of QRH Procedures

The QRH procedures for rudder malfunctions were first introduced in January 1997. Since then they have changed several times, either to simplify the procedures or as a result of hardware changes. They still have many branches depending upon the RSEP status of the aircraft and what condition is detected by the crew.
An uncommanded rudder deflection and/or hardover may be caused by a number of different failure modes within the rudder PCU and/or yaw damper, and the severity of symptoms could differ widely from a nuisance yaw damper deflection to a full-scale rudder hardover resulting in reduced controllability. As identification of the primary cause of such a failure may be impossible in flight, certain procedures have been mandated which aim to minimize the effects of the malfunction. There are two similar QRH drills which cover this situation:

JAMMED OR RESTRICTED FLIGHT CONTROLS
Condition: Movement of the elevator, aileron/spoiler or rudder is restricted
UNCOMMANDED RUDDER/YAW OR ROLL
Condition: Uncommanded rudder pedal displacement or pedal kicks or uncommanded yaw or roll.

The latter is more appropriate for a rudder hardover, but either procedure will direct you to the correct solution.

AUTOPILOT (if engaged)…………………..DISENGAGE
AUTOTHROTTLE (if engaged)……………DISENGAGE
Verify thrust is symmetrical.
These are the only recall items. First disengage the automatics, get control of the flight path and verify thrust is symmetrical. If you have a STBY RUD ON light installed (and serviceable), ie an RSEP a/c, then go to the JAMMED OR RESTRICTED FLIGHT CONTROLS checklist. The logic here is that the FFM will either have detected an opposing pressure between A & B actuators and activated the standby rudder PCU or there was no opposing pressure and the problem was a jam rather than a hydraulic problem.
The rest of this section assumes that you do not have a STBY RUD ON light installed (ie Pre-RSEP a/c).
YAW DAMPER……………………………..OFF
The yaw damper is switched OFF. This removes power to the yaw damper actuator, therefore eliminating any input to the main rudder PCU. Whilst this should eliminate any nuisance yaw and secondary roll caused by a failure within the yaw damper or coupler, with its limited authority over main rudder panel deflection it is highly questionable whether this alone could produce a large-scale uncommanded rudder movement.
If the yaw or roll is the result of uncommanded rudder displacement or pedal kicks:
Rudder trim………………………………….Center
Rudder pedals………………………………..Free & center
After verifying zero rudder trim, the checklist calls for a maximum combined effort of both pilots to centre the rudder pedals. The intention of this is to provide a maximum force to shear any metal fragments or “chips” which may be present within the servo-valve. Remember, centred pedals mean a centralised rudder.
If rudder pedal position and/or movement are not normal:
SYSTEM B FLIGHT CONTROL switch….STBY RUD
During a normal flight phase, the rudder has three separate sources of power; A-system hydraulics, B-system hydraulics and Standby hydraulics. The objective of any such drill would be to reduce the uncommanded deflection of the rudder panel, and to restore some directional controllability. This is achieved within the drill by first reducing the authority of the main rudder PCU by removing the B-system hydraulic source. A-system pressure remains, but at a considerably reduced pressure due to the functioning of the RPR / load limiter, hence blowdown will help to realign the control surface. Re-positioning the B-system flight controls switch to standby rudder removes B-system hydraulic pressure from the main rudder PCU, and provides a completely independent method of rudder panel control through the standby rudder PCU, further assisting in re-alignment of the control surface.

BOEING 737 FLIGHT DECK

In the NG, the larger PFD/ND (formerly known as EFIS/MAP) are now side by side to fit into the space available, controls for these are located either side of the MCP. The EIS & fuel gauges are both on the central CDS with a sixth screen below that, between the CDU's. The flat panel displays have the advantage over CRT's of being lighter, more reliable and consume less power, although they are more expensive to produce.

The overhead panel remains largely unchanged since the -100, apart from a digital AC & DC metering panel & DCPCS.
According to Boeing, the requirements from the airlines for the new cockpit were:

• To be easy for current 737 pilots to operate.
• To anticipate future requirements eg transitioning to 777 style flightdecks.
• To accommodate emerging navigation and communication technologies.

For an in-depth look at the NG flightdeck, follow this link to the article in Aero No.04 from Boeing

727  |  737-100  |  737-200  |  737-3/4/500

Photos of Boeing 737 Engine

The left hand side of the CFM56-3. The large silver coloured pipe is the start air manifold with the starter located at its base. The black unit below that is the CSD. The green unit forward (left) of the CSD is the generator cooling air collector shroud, the silver-gold thing forward of that (with the wire bundle visible) is the generator, and the green cap most forward is the generator cooling air inlet.

The view into the JT8D jetpipe.

The corrugated ring is the mixer unit, this is designed to thoroughly mix the bypass air with the turbine exhaust.

The exhaust cone makes a divergent flow which slows down the exhaust and also protects the rear face of the last turbine stage.

The view into the CFM56-3 jetpipe.
This is the turbine exhaust area, no mixing is required as the bypass air is exhausted coaxially

There are two fan inlet temperature sensors in the CFM56-3 engine intake. The one at the 2 o'clock position is used by the PMC and the one at the 11 o'clock position is used by the MEC. The MEC uses the signal to establish parameters to control low and high idle power schedules.

The temperature data is used for thrust management and variable bleed valves, variable stator vanes & high / low pressure turbine clearance control systems.

The CFM56-7 inlet has just one fan inlet temperature probe, which is for the EEC (because there is no PMC on the NG's).
A subtle difference between the NG & classic temp probes is that the NG's only use inlet temp data on the ground and for 5 minutes after take-off. In-flight after 5 minutes temp data is taken from the ADIRU's.
The temperature data is used for thrust management and variable bleed valves, variable stator vanes & high / low pressure turbine clearance control systems

The CFM56-7 spinner has a unique conelliptical profile. The first 737-3/400's had a conical (sharp pointed) spinner but these tended to shed ice into the core. This was one of the reasons for the early limitation of minimum 45% N1 in icing conditions which made descent management quite difficult. They were later replaced with elliptical (round nosed) spinners which succeeded in deflecting the ice away from the core, but because of their larger stagnation point, were more prone to picking up ice in the first place. The conelliptical spinner of the NG's neatly solves both problems

The CFM56-7 tailpipe is slightly longer then the CFM56-3 and has a small tube protruding from the faring. This is the Aft Fairing Drain Tube for any hydraulic fluid, oil or fuel that may collect in there. There is also a second drain tube that does not protrude located on the inside of the fairing.

The JT8D tailpipe fitted as standard from l/n 135 onwards.
The original thrust reversers were totally redesigned by Boeing and Rohr since the aircraft had inherited the same internal pneumatically powered clamshell thrust reversers as the 727 which were relatively ineffective and apparently tended to lift the aircraft off the runway when deployed! The redesign to external hydraulically powered target reversers cost Boeing $24 million but dramatically improved its short field performance which boosted sales to carriers proposing to use the aircraft as a regional jet from short runways. Also the engine nacelles were extended by 1.14m as a drag reduction measure

The outboard side of the JT8D-9A with the cowling open.

Reverse Thrust

he original 737-1/200 thrust reversers were pneumatically powered clamshell doors taken straight from the 727 (shown left). When reverse was selected, 13th stage bleed air was ported to a pneumatic actuator that rotated the deflector doors and clamshell doors into position. Unfortunately they were relatively ineffective and apparently tended to push the aircraft up off the runway when deployed. This reduced the downforce on the main wheels thereby reducing the effectiveness of the wheel brakes.

By 1969 these had been changed by Boeing and Rohr to the much more successful hydraulically powered target type thrust reversers (shown right). This required a 48 inch extension to the tailpipe to accommodate the two cylindrical deflector doors which were mounted on a four bar linkage system and associated hydraulics. The doors are set 35 degrees away from the vertical to allow the exhaust to be deflected inboard and over the wings and outboard and under the wings. This ensures that exhaust and debris is not blown into the wheel-well, nor is it blown directly downwards which would lift the weight off the wheels or be re-ingested. Fortunately the new longer nacelle improved cruise performance by improving internal airflow within the engine and also reduced cruise drag. These thrust reversers are locked against inadvertent deployment by both deflector door locks and the four bar linkage being overcenter. To illustrate how poor the original clamshell system was, Boeings own data says target type thrust reversers at 1.5 EPR are twice as effective as clamshells at full thrust!

The CFM56 uses blocker doors and cascade vanes to direct fan air forwards. Net reverse thrust is defined as: fan reverser air, minus forward thrust from engine core, plus form drag from the blocker door. As this is significantly greater at higher thrust, reverse thrust should be used immediately after landing or RTO and, if conditions allow, should be reduced to idle by 60kts to avoid debris ingestion damage. Caution: It is possible to deploy reverse thrust when either Rad Alt is below 10ft – this is not recommended

The REVERSER light shows either control valve or sleeve position disagreement or that the auto-restow circuit is activated. This light will illuminate every time the reverser is commanded to stow, but extinguishes after the stow has completed, and will only bring up master caution ENG if a malfunction has occurred. Recycling the reverse thrust will often clear the fault. If this occurs in-flight, reverse thrust will be available after landing.

The REVERSER UNLOCKED light (EIS panel) is potentially much more serious and will illuminate in-flight if a sleeve has mechanically unlocked. Follow the QRH drill, but only multiple failures will allow the engine to go into reverse thrust.

The 737-1/200 thrust reverser panel has a LOW PRESSURE light which refers to the reverser accumulator pressure when insufficient pressure is available to deploy the reversers. The blue caption between the switches is ISOLATION VALVE and illuminates when the three conditions for reverse thrust are satisfied: Engine running, Aircraft on ground & Fire switches in normal position. The guarded NORMAL / OVERRIDE switches to enable the reverse thrust to be selected on the ground with the engines stopped (for maintenance purposes).

Huskit

The first "hushkit" was not visible externally, in 1982 exhaust mixers were made available for the JT8D-15, -17 or -17R. These were fitted behind the LP turbine to mix the hot gas core airflow with the cooler bypassed fan air. This increased mixing reduced noise levels by up to 3.6 EPNdB.
Several different Stage III hushkits have been available from manufacturers Nordam (shown right) and AvAero since 1992. The Nordam comes in HGW and LGW versions.
As hushkits use more fuel, the EU tried to ban all hushkitted aircraft flying into the EU from April 2002. This was strongly opposed and the directive has been changed to allow hushkitted aircraft to use airports which will accept them.
737 classics may be fitted with hardwall forward acoustic panels which reduce noise by 1 EPNdB