WARNING SYSTEMS

Warning Lights       Master Caution and System Annunciator lights, left and right.   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. Keying of warning lights   Red lights - Warning - indicate a critical condition and require immediate action. Amber lights - Caution - require timely corrective action. Blue lights - Advisory - eg valve positions and unless bright blue, ie a valve/switch disagreement, do not require crew action. Green lights - Satisfactory - indicate a satisfactory or ON condition.

Aural Warnings Cockpit aural warnings include the fire bell, take-off configuration warning, cabin altitude, landing gear configuration warning, mach/airspeed overspeed, stall warning, GPWS and TCAS. External aural warnings are: The fire bell in the wheel well and the ground call horn in the nose wheel-well for an E & E bay overheat or IRS’s on DC. Only certain warnings can be silenced whilst the condition exists. To test the GPWS, ensure that the weather radar is on in TEST mode and displayed on the EHSI. Pressing SYS TEST quickly will give a short confidence test, pressing for 10 seconds will give a full vocabulary test.   The GPWS pane. AURAL WARNING PRIORITY LOGIC MODE PRIORITY DESCRIPTION ALERT LEVEL 7 1 WINDSHEAR WINDSHEAR WINDSHEAR W 1 2 PULL-UP (SINK RATE) W 2 3 PULL-UP (TERRAIN CLOSURE) W 2A 4 PULL-UP (TERRAIN CLOSURE) W V1 5 V1 CALLOUT I TA 6 TERRAIN TERRAIN PULL-UP W WXR 7 WINDSHEAR AHEAD W 2 8 TERRAIN TERRAIN C 6 9 MINIMUMS I TA 10 CAUTION TERRAIN C 4 11 TOO LOW TERRAIN C TCF 12 TOO LOW TERRAIN C 6 13 ALTITUDE CALLOUTS I 4 14 TOO LOW GEAR C 4 15 TOO LOW FLAPS C 1 16 SINK RATE C 3 17 DONT SINK C 5 18 GLIDESLOPE C WXR 19 MONITOR RADAR DISPLAY C 6 20 APPROACHING MINIMUMS I 6 21 BANK ANGLE C TCAS 22 RA (CLIMB, DESCEND, ETC.) W TCAS 23 TA (TRAFFIC, TRAFFIC) C TEST 24 BITE AND MAINTENANCE INFORMATION I Radio Altimeter Callouts Automatic rad-alt calls are a customer option on the 3-900 series. Calls can include any of the following: 2500 ("Twenty Five Hundred" or "Radio Altimeter"). 1000 500 400 300 200 100 50 40 30 20 10 "Minimums" or "Minimums, Minimums" "Plus Hundred" when 100ft above DH "Approaching Minimums" when 80ft above DH "Approaching Decision Height" "Decision Height" Customers can also request special heights, such as 60ft. Noise Levels If is often commented how loud these callouts are. The volume level for these callouts and any other aural warnings is set so that they can still be audible at the highest ambient noise levels, this is considered to be when the aircraft is at Vmo (340kts) at 10,000ft. The design sound pressure level at 35,000ft, M0.74, cruise thrust is 87dB at the Captains seat, compared to 90-93dB in the cabin. Many pilots consider the 737 flightdeck to be generally loud. This is Boeings response to that charge: "Using the flight deck noise levels measured by Boeing Noise Engineering during a typical flight profile (entire flight), a daily A-weighted sound exposure was calculated using ISO/DIS 1999 standards. This calculation indicates the time weight noise exposure is below 80 db(A) and should not cause hearing damage. Flight deck noise improvement continues to be a part of current Boeing product quality improvement activities." And when asked later about the particularly noisy NG: "Boeing has conducted extensive flight tests to define the contributing noise sources for the 737 Flight Deck. Subsequently, various system and hardware modifications have been evaluated for possible improvements. Currently there are no proposed changes where the benefits are significant enough to warrant incorporation. Additional candidates are currently under study and if their merit is validated, they could be incorporated at a later date during production and retrofit." That said, in 2005 Boeing added 10 small vortex generators at the base of the windscreen which reduce flightdeck aerodynamic noise by 3dB. (See fuselage page for photo).

Stall Warning Stall warning test requires AC power. Also, with no hydraulic pressure, the leading edge flaps may droop enough to cause an asymmetry signal, resulting in a failure of the stall warning system test. If this happens, switch the "B" system electric pump ON to fully retract all flaps and then repeat the test. System test switches on the aft overhead panel The 737-1/200's had a different stall warning panel as shown right: The OFF light may indicate either a failure of the heater of the angle of attack sensor a system signal failure or a power failure. The test disc should rotate, indicating electrical continuity, when the switch is held to the test position. 737-200 Stall Warning Panel

TCAS Various versions of TCAS have been fitted to the 737 since its introduction in the 1990's. The early days of TCAS there were different methods of displaying the visuals. For the Honeywell system (Previously AlliedSignal, previous to that - Bendix/King), their most popular method for non-EFIS airplanes was to install an RA/VSI which was a mechanical VSI that had the "eyebrows" on the outer edge directing the pilot to climb (green) or stay away from (red) and use the separate Radar Indicator for the basic traffic display. Even early EFIS aircraft had the RA/VSI (see photos left & right) TCAS is now integrated at production into the EFIS displays. The PFD/EADI will display advisories to climb, descend, or stay level since they give the vertical cue to the pilot. The ND/EHSI provides the map view looking down to show targets and their relative altitude and vertical movement relative to your aircraft.   TCAS display integrated onto the ND

TCAS control is from the transponder panel.

Weather Radar The beamwidth of the 737 weather radar is 3.5 degrees. To calculate the height of the cloud tops above your altitude use the following formula: Cloud tops above a/c (ft) = range (nm) x (tilt - 1.5 deg) x 100 eg Wx at range 40nm stops painting at +2deg tilt. The tops would be 40 x 0.5 x 100 = 2000ft above your level. Weather radar or terrain can be overlaid onto the EHSI with these switches on the classics. In the NG the overlay switches are part of the EFIS control panel. The colours may appear similar but their meanings are very different. 737 NG's are fitted with predictive windshear system (PWS). This is available below 2300ft. You do not need weather radar to be switched on for PWS to work, since it switches on automatically when take-off thrust is set. However there is a 12 sec warm up period, so if you want PWS available for the take-off you should switch the weather radar on when you line up. Windshear warning displayed on the ND. Notice the cone and range at which windshear is predicted. EGPWS - Peaks Display The Peaks display overlays EGPWS terrain information onto the EHSI. The colour coding is similar to wx radar but with several densities of each colour being used. The simplified key is: Color Altitude Diff from Aircraft (ft) Black No terrain Cyan Zero ft MSL (Customer option) Green -2000 to +250 Yellow -500 to +2000 Red +2000 or above Magenta Terrain elevation unknown The two overlaid numbers are the highest and lowest terrain elevations, in hundreds of ft amsl, currently being displayed. Here 5900ft and 800ft amsl. One of the main difference between Peaks display and others is that it will show terrain more than 2000ft below your level (eg a mountain range from cruise altitude). This can be very useful for situational awareness. EGPWS Limitations Do not use the terrain display for navigation. Do not use within 15nm of an airfield not in the terrain database. Honeywell EGPWS Pilots notes

Proximity Switch Electronic Unit The Proximity Switch Electronic Unit (PSEU) is a system that communicates the position or state of system components eg flaps, gear, doors, etc to other systems. The 737-NG's are fitted with a PSEU which controls the following systems: Take-off and landing configuration warnings, landing gear transfer valve, landing gear position indicating and warning, air/ground relays, airstairs & door warnings and speedbrake deployed warning. The PSEU light is inhibited from when the thrust levers are set for take-off power (thrust lever angle beyond 53 degrees) until 30 seconds after landing. If the PSEU light illuminates, you have a "non-dispatchable fault" and the QRH says do not take-off. In this condition the PSEU light can only be extinguished by fixing the fault. However if you only get the PSEU light on recall, you have a "dispatchable fault" which it is acceptable to go with. In this condition the PSEU light will extinguish when master caution is reset. SFP aircraft (-800SFP / -900ER) also have an SPSEU which monitors the 2 position tailskid.

LANDING GEAR

General

The landing gear on the NG has been extensively redesigned. The nose gear is 3.5" longer to relieve higher dynamic loads and the nose-wheelwell has been extended 3" forward. The main gear is also longer to cater for the increased fuselage lengths of the -8/900 series and is constructed from a one piece titanium gear beam based on 757/767 designs. There is an externally mounted trunnion bearing on the gear, a re-located gas charging valve, and the uplock link is separate from the reaction link. It is fitted with 43.5" tyres and digital antiskid.

Unfortunately the 737-700 was particularly prone to a dramatic shudder from the main landing gear if you tried to land smoothly. Fortunately Boeing started fitting shimmy dampers to this series from L/N 406 (Nov 1999) and a retrofit was made available.

One of the peculiarities of the 737 is that it invariably appears to crab when taxying. Theories for this include: A slightly castoring main gear to increase the crosswind capability; Play in the scissor link pins; Weather-cocking into any crosswind impinging on the fin; Torque reaction from the anti-collision light !!! Engineers will tell you that is due to the main gear having a couple of degrees of play due to the shimmy dampers.

 

 

Tyres

Tyres are tubeless and inflated with nitrogen. Pressures vary with series, maximum taxi weight, temperature and size of tyres. Unfortunately this large variation in tyre pressures makes it difficult to know your aquaplaning speed. The table below should prove helpful, notice how the aquaplaning speeds are all just below the typical landing speeds. Note: Once aquaplaning has started, it will continue to a much lower speed.

Series	Main Gear	Aquaplaning Speed	Nose Gear	Aquaplaning Speed
Originals	96 - 183psi	84 - 116Kts	125 - 145psi	96 - 104Kts
Classics	185 - 217psi	118 - 128Kts	163 - 194psi	111 - 121Kts
NG's	117 - 205psi	93 - 123Kts	123 - 208psi	95 - 124Kts

Another oddity of the 737 is the resonant vibration during taxying that occurs at approx 17kts in classics and 24kts in NG's. This is due to tyre "cold set". This is a temporary flat spot that occurs in tyres with nylon chord (ie all Boeing tyres) when hot tyres are parked and they cool to ambient temperature. Hence the reason why the flat spot is most pronounced in cold weather and tends to disappear during taxying as the tyres warm up again.

The speed rating of all tyres is 225mph (195kts).

 

 

Gear Seals

Notice that none of the 737 series have ever had full main gear doors. Instead the outer wall of the tyres meet with aerodynamic seals in the wheel well to make a smooth surface along the underside of the aircraft. The first few 737's had inflatable seals which were inflated by bleed air when the gear was either up or down and deflated during transit. The landing gear panel had a NOT SEALED caption which would illuminate during transit (normal), if it illuminated at any other time you could have a puncture and the seal could be depressurised with the GEAR SEAL SHUTOFF switch to save bleed requirements.

These were soon dropped as being too complicated and a similar drag and noise advantage was achieved with the present fixed rubber seals.

 

Brakes

The standard 737 brakes are a steel alloy called Cerametalix(R) with versions made by either Goodrich or Honeywell. Since 2008 the 737NG has had a carbon brake option from either Goodrich with Duracarb(R) or Messier-Bugatti with SepCarb® III-OR. They are both about 300kgs lighter than steel and last twice as long.

The brake pressure gauge merely shows the pressure of the air side of the accumulator and should normally indicate 3000psi. The normal brake system and autobrakes are powered by hydraulic system B. If brake pressure drops below 1500psi, hydraulic system A automatically provides alternate brakes which are manual only (ie no autobrake) and the brake pressure returns to 3000psi. Antiskid is available with alternate brakes, but not touchdown or locked wheel protection on series before the NG's.

If both system A and B lose pressure, the accumulator isolation valve closes at 1900psi and you are just left with residual hydraulic pressure and the pre-charge. The gauge will indicate approx 3000psi and should provide 6 full applications of brake power through the normal brake lines (so full antiskid is available) As the brakes are applied the residual pressure reduces until it reaches 1000psi at which point you will have no more braking available.

If the brake pressure gauge ever shows zero, this merely indicates that the pre-charge has leaked out, normal and alternate braking are unaffected if you still have the hydraulic systems (see QRH). The accumulator also provides pressure for the parking brake.

Note that on the 737-1/200, hydraulic system A operates the inboard brakes and system B operates the outboard brakes. Both brake pressures are indicated on the single hydraulic brake pressure gauge.

There are four thermal fuse plugs in the inner wheel half which prevent tyre explosion caused by hot brakes. The plugs melt to release tyre pressure at approx 177C (351F).

Brake Pressure Indication (psi)	Condition
3000	Normal.
3000	No hydraulics, minimum 6 applications of brakes available with accumulator.
1000	No hydraulics, accumulator used up.
Zero	No pre-charge, normal braking available with hydraulics.

Brake Accumulator

Brake Wear Pin

 

 

 

Autobrakes

Autobrake Selector	Max Pressure at Brakes (PSI)	Deceleration Rate (ft/sec²)
1	1250	4
2	1500	5
3	2000	7.2
Max	3000	12 (below 80kts)
“	“	14 (above 80kts)
RTO	Full	Not Controlled

There is an "on ramp" period where autobrake pressure is applied over a period of time. Approximately 750psi is applied in 1.75 sec, then the pressures above are reached in another 1.25sec for autobrakes 1, 2, or 3 and approx. 1.0 sec for autobrake MAX. 

Notice from the table above that autobrake Max does not give full brake pressure. For absolute maximum braking on landing, select autobrake Max to assure immediate application after touch down then override with full toe brake pressure. 

Using high autobrake settings with idle reverse is particularly hard on the brakes as they will be working for the given deceleration rate without the assistance of full reverse thrust.

To cancel the autobrake on the landing roll with toe brakes you must apply a brake pressure in excess of 800psi (ie less than that required for autobrake 1). This is more difficult on the NG's because the feedback springs on the brake pedals are stiffer. Autobrake can also be cancelled by putting the speedbrake lever down or by switching the autobrake off. I would advise against the latter in case you accidentally select RTO and get the full 3000psi of braking!

Occasionally you may see the brakes (rather than the cabin crew!) smoking during a turnaround. This may be due to hard braking at high landing weights. But the most common reason is that too much grease is put on the axle at wheel change so that when the wheel is pushed on, the grease is deposited inside the torque tube; when this gets hot, it smokes. It could also be contamination from hydraulic fluid either from bleeding operation or a leak either from the brakes or another source.

Photos

	The landing gear panel is located between  the engine instruments and F/O's instrument panel. The Green lights tell you that the gear is down and locked and the red lights warn you if the landing gear is in disagreement with the gear lever position. With the gear UP and locked and the lever UP or OFF, all lights should be extinguished. On a couple of occasions I have seen 3 reds and 3 greens after the gear has been selected down. This was because the telescopic gear handle had not fully compressed back toward the panel. If this happens to you, give it a tap back in and the red lights will extinguish.
	737's used for cargo operations have an extra set of green "GEAR DOWN" lights on the aft overhead panel. This is because with the cabin filled with freight, the main gear downlock viewer could not be guaranteed to be accessible in-flight. The NG's also have these lights because they do not have gear downlock viewers installed.
Main gear viewer (not NG's)	If any green gear lights do not illuminate after the gear is lowered, you might consider a visual inspection through the gear viewers. The main gear viewer is in the cabin and the nose gear viewer is on the flight deck. The main gear viewers are not installed on NG series aircraft. This is the main gear viewer and it is located in the isle, just behind the emergency exit row. The first time you look through a viewer it will probably take you several minutes to find what you are looking for, hardly ideal if you are in the situation for real so it is worth acquainting yourself with its use.
Main gear viewer prisms (not NG's)	There are two prisms, one for each main gear leg. Don't forget to switch on the wheel-well light if at night.
Gear locked marks (not NG's)	Eventually, you should be able to see three red marks on the undercarriage, if they line up then your gear is certainly down and probably locked.
Main wheel-well and downlock viewer (classics)	The location of the main gear downlock viewer in the wheel well can be clearly seen in this photograph.
Nosegear viewer (not NG's)	The nosegear viewer is located under a panel toward the aft of the flightdeck. There is no prism, just a long tube. This viewer directs your eye exactly toward the correct place for viewing but is usually more dirty. The nosegear down marks are two red arrows pointing at each other.
Manual gear extension access hatch	If the gear fails to extend properly or hydraulic system A is lost, the gear can be manually extended by pulling the manual gear extension handles, located in the flight deck. This should be done in accordance with the QRH procedure. On NG aircraft opening this hatch affects the operation of landing gear extension & retraction.
Tyre damage fitting - NG only	This pin is designed to detect any loose tyre tread during gear retraction. If any object impacts on it during retraction, then the gear will automatically extend. The affected gear cannot be retracted until this fitting is replaced. There is one pin at the aft outside of each main wheel well.
Other landing gear system photographs
Nosewheel door (classic)	Gravel Deflector (-200)
Nose wheel	Tail skid (-400)

ICE AND RAIN PROTECTION

Panels
737-1/200 Ice & Rain Panel	737-3/4/500 Ice & Rain Panel	737-NG Ice & Rain Panel
Differences: No alpha vanes WAI has ground test position Engine anti-ice captions are: COWL VALVE OPEN, R VALVE OPEN, L VALVE OPEN.	Alpha vanes added Now only one temp probe (many 1/200's had two) TAT TEST button (ie aspirated probe). NB if there is no TAT TEST button you have an unaspirated probe.	Static ports not heated Aux pitot added.
Window Heat If window heat is switched ON but the ON light is extinguished, this means that heat is not being applied to the associated window. This could be because the heat controller has detected that the window is becoming overheated (normal on hot days in direct sunlight) and can be verified by touching the window. The heat will automatically be restored when the window has cooled down. To verify that window heat is still available a PWR TEST should illuminate all ON lights if the window heat switches are ON. The PWR TEST forces the temperature controller to full power but overheat protection is still available.  If an OVERHEAT light illuminates, either a window has overheated or electrical power to the window has been interrupted. The affected window heat must be switched OFF and allowed 2-5mins to cool before switching ON again. The OVHT TEST simulates an overheat condition.
Wing Anti Ice Wing anti-ice (WAI) is very effective and is normally used as a de-icing system in-flight, in applications of 1 minute. On the ground it should be used continuously in icing conditions. The WAI switch logic is interesting, on the ground, bleed air for WAI will cut-off if either thrust lever is above the take-off warning setting, but will be restored after the thrust is reduced. This allows you to perform engine run-ups etc without having to check that the WAI is still on afterwards. The switch is solenoid held and will trip off at lift-off, this is for performance considerations as the bleed air penalty is considerable. Note that on early systems, ie those with a GND TEST position, with the WAI switch ON on the ground, the WAI is inhibited until lift-off ie "armed", This is opposite to the present system. WAI, unlike engine AI, uses bleed air from the main pneumatic manifold, this is to ensure a source of bleed air during engine out operations. Only the leading edge slats have WAI (ie not leading edge flaps). The NG series outboard slat has no wing anti-ice facility (see photo) believed to be due to excessive bleed requirements. However in June 2005 it was announced that the 737-MMA will have raked wingtips with anti-ice along the full span. This is because the MMA will be spending long periods of time on patrol at low level where it will be exposed to icing conditions. NB Where QRH ENGINE FAILURE/SHUTDOWN drills ask “If wing anti-ice is required:”, if icing conditions are anticipated, these actions should be completed in preparation for WAI use to prevent asymmetric application. There is no bleed penalty for this reconfiguration until WAI is actually used. On the NG, if WAI is used for more than 5 secs in-flight, the SMYD will adjust the stick shaker speeds and manouvre speed bars to allow for airframe ice. Photo: Wing ice on the outboard slat of a 737-700
Engine Anti Ice Engine anti-ice (EAI) heats the engine cowl to prevent ice build-up, which could break off and enter the engine. The 3/4/500 spinner was originally conical to prevent ice buildup but was changed to an elliptical shape to deflect ice away from the engine core. The NG's have the best of both worlds with a coneliptical shaped spinner (see photo left) that does both jobs. EAI should be used continuously on the ground and in the air in icing conditions. It uses 5th stage bleed air, augmented by 9th stage as required, from the associated engine. COWL ANTI-ICE lights will illuminate if an overtemp of >440C (not NGs) or overpressure >65psig condition exists in either duct. In this situation thrust on the associated engine should be reduced until the light extinguishes. Wing and engine VALVE OPEN lights use the bright blue/dim blue - valve position in disagreement / agreement logic. The wing L and R VALVE OPEN lights in particular may remain bright blue after start and during taxy. This is because they are pneumatically operated, they can be made to open with a modest amount of engine thrust.
Airframe Visual Icing Cues An ice detection system is an option that is rarely taken up on the 737 so it is up to the crew to spot ice formation and take the necessary action. The following photos show some of the places where ice accretion is visible from the flight deck. Note engine anti-ice should be used whenever the temperature and visible moisture criteria are met and not left until ice is seen, to avoid inlet ice build up which may shed into the engine.
Under the windscreen wiper blades. This is one of the first places that ice will form, precipitation falls on the bottom of the windscreen and runs up to the wipers. This is not an accurate indication of the amount of icing on the airframe because of the stagnation point where the blade and windscreen meet and also because the windscreen is heated. I would describe conditions where ice forms here as LIGHT ICING.
On the wiper nut This is my preferred indication of airframe ice accretion. If ice is seen here it is surely also on other parts of the airframe. The weight and aerodynamic effect of all this ice on the the airframe and control surfaces is why there is the "residual ice" penalty of several tons on the landing performance graphs "If operating in icing conditions during any part of the flight when the forecast landing temperature is below 8C, reduce the normal climb limited landing weight by xxxxkg." (FPPM 1.3.3). I would describe conditions where ice forms here as MODERATE ICING.
On the central windscreen pillar For ice to form on a flat heated windscreen, conditions must be bad. You can see how the shape of the formation follows the airflow lines. You can imagine how much ice is on the rest of the aircraft, especially when you consider that most of it is unheated, particularly on the fin and stabiliser. Vol 1 SP.16.8 states "Avoid prolonged operation in moderate to severe icing conditions." This photo was taken at about 20,000ft climbing through the tops of rain bearing frontal cloud. The ice shown here formed in under a minute. I would describe conditions where ice forms here as SEVERE ICING.
Non-environmental Icing The NG's have a problem with frost forming after landing on the wing above the tanks where fuel has been cold soaked. This is officially known as "Wing upper surface non-environmental icing". The reason is the increased surface area of the fuel that comes into contact with the upper surface of the wing. This is because the shape of the wing fuel tanks was changed (moved outboard) to accommodate the longer landing gear that was in turn required for the increased fuselage lengths of the NG family to reduce the risk of tailstrikes! The only solution until recently has been to limit your arrival fuel to less than approx 4,000kg. Now Boeing have issued guidelines on the acceptable location and amount of upper wing frost. The Boeing advice is as follows: "Flight crews should visually inspect the lower wing surface. If there is frost or ice on the lower surface, outboard of measuring stick 4, there may also be frost or ice on the upper surface. The distance the frost extends outboard of measuring stick 4 can be used as an indication of the extent of frost on the upper surface. It should be noted that if the thickness of the frost on the lower surface of the wing is 1/16 inch (1.5 mm) thick or less, the thickness of the frost on the upper surface will be less than 1/16 inch (1.5 mm) thick. If the thickness of the frost on the lower surface is greater than 1/16 inch (1.5 mm), then a physical inspection of the upper surface frost is required."
737-1/200 737-1/2/3/4/500 737-NG	Wiper Controls One of the most welcome features of the 737-NG is the improvement to the windscreen wipers. The wipers are now independent, have an intermittent position and best of all - are almost silent. Rain Repellent The rain repellent has been removed due to worries about the environmental effects of the "RainBoe" fluid used as it contains CFC's. It is also poisonous and in 1991 Boeing added D-limonine which has a strong smell of orange peel into RainBoe so that leakage could be detected. There are no plans to replace the rain repellent with another liquid product even though there are safe alternatives eg "Le Bozec". On 25 May 1982, a 737-200Adv (PP-SMY) was written off by a heavy landing in a rainstorm. One report stated that "The pilots misuse of rain repellent caused an optical illusion". Since early 1994 all Boeing aircraft have been built with Surface Seal coated glass from PPG Industries which has a hydrophobic coating. The coating does deteriorate with time depending upon wiper use and windscreen cleaning methods etc, but can be re-applied.
Check out this video of a 737-900 DV window opening during the take-off roll during flight testing. Notice that a high speed abort is not necessary if the DV window opens. Limitations Engine anti-ice must be on when icing conditions exist or are anticipated, except during climb and cruise below -40°C SAT. Use of wing anti-ice above FL350 may cause bleed trip off and possible loss of cabin pressure. (SP.16.8)

AUTOMATIC FLIGHT

The glareshield panel, commonly referred to as the MCP, contains not only the Mode Control Panel, but also the master caution lights & annunciations, fire warning lights and, on the NG's, the EFIS control panels. Whilst the MCP has evolved with the autopilot, the master caution and fire warning lights have remained unchanged through to the present day which is testimony to its good initial design.

707 The original purpose of the glareshield panel was to put the most important warning lights in the most attention grabbing place. The glareshield panel is the only thing at eye level, so the fire panel was put there. (Photo: Paolo DeAngelis, Munich)

727-200adv These 727-200 Adv panels start to combine the fire panel from the 707 with the automatic systems of the early 737's. From left to right you have a rudimentary master caution system (above) or cargo fire (below); autothrottle (above); flight director and fire panel. In the later production 727's the fire switches were moved down to the centre console leaving more room for autopilot & flight director panels and the glareshield panel became identical to the 737-200. (Photo: Mike Olson, Airliners.net)

737-100/200

The 737 saw the fire panel relegated to the throttle quadrant to allow space for the master caution, flight director and autopilot controls. This was the original MCP as fitted to the -100/-200's with the Sperry SP-77 autopilot. They comprised three panels, the autopilot (centre) and one for each flight director (sides). All three were independent so any mode to be used with the autopilot (eg ALT HOLD or VOR/LOC) had to be selected three times. HDG SEL and VOR/LOC could be coupled to the autopilot but would only be driven by the heading bug set on the Captains compass and the course set on the Captains HSI. The SP-77 autopilot consisted of a Pitch Control Computer and a Roll Computer. For a dual-channel configuration, there were two Pitch Computers. Airplanes with this configuration had separate Flight Director controllers for the FD-108, FD-109, or FD-110 system, whichever was installed. The FD controllers were either built into the ADIs and HSIs, or were of various shapes and sizes with different combinations of switches and position nomenclatures. Modes available were GA, OFF, HDG, VOR LOC, AUTO APP & MAN GS, which was mainly used for capturing the glideslope from above!. There is also a PITCH CMD knob which has now become vertical speed. The centre panel is for autopilot selections and has two paddles to engage/disengage the ailerons and elevators "AIL" & "ELEV" for roll and pitch modes and could be engaged separately or together. The LH knob has the roll modes of HDG, VOR LOC, AUTO APP & MAN G/S and has a HDG OFF / HDG SEL switch to its right (see para 1). The RH knob has pitch modes of ALT HOLD or TURB. The TURB mode was controlled by the vertical gyro to allow smoother movements to regain altitude during turbulence. Some also had an ALT SEL mode. The small knob at the top, left of centre labelled "A", "B", "AB", is the hydraulic system selector source for the autopilot. Virtually none of the early 737-1/200's had ALT Select or Speed Select and were flown most of the time in CWS (Control Wheel Steering) - it was used like a sort of sophisticated  "wing leveller". The A/P was then "Flown" via the normal controls.

737-100/200 option

This asymmetric looking version of the MCP, was the first to have heading and course windows. Although everything looks biased to the LHS it is more First Officer friendly because he can set a heading (centre window) or course (the two outside windows) on this panel rather than having to rely on what the Captain sets on his compass or HSI. The usual F/D MODE SEL, ALT HOLD & PITCH CMD controls are all in this single panel and are repeated to both the Capt's and F/O's F/D's. The autopilot panel is displaced to the right.

737-200Adv

Toward the end of its production run, the Adv was fitted with an SP177 autopilot with integrated PDCS/FMC and automatics and in 1982 became Cat IIIa autoland capable. The Adv mode control panel has remained virtually unchanged through to the NG's. The differences between this -200Adv MCP and the -300+ MCP are: EPR button became N1 VNAV/PDC became VNAV No ALT or SPD INTV buttons fitted. Number tapes in windows instead of LCD's

737-300/400/500

The classics were fitted with Sperry SP-300 autopilot-flight director system (AFDS). This early -300 panel has paddles to engage & disengage autopilots and CWS. The two small grey panels either side of the MCP are to select the source of navigation information. The options are FMC (normal mode), ANS-L or ANS-R if the alternate navigation system (IRS based) is required.On pre-1991 MCP's, turning the altitude knob changed MCP altitude in 1000ft increments, when pressed in it changed to 100ft increments. Differences between various MCP's are: The A/P CMD/CWS/Disengage paddles changing to select buttons, or a mixture of both (see below). ALT & SPD INTV buttons for FMC hard speed and alt restraints, (covered by blanking plates with some operators).

This -500 has no ANS so those side panels are missing. They are replaced in this aircraft by stopwatch buttons, much more useful! The two blanking plates in the MCP are for the SPD INTV & ALT INTV options.

737-NG

The basic Honeywell (formerly Sperry) MCP is virtually unchanged from the 200ADVs but the EFIS control panels have been moved into the glareshield from the aft electronics panel in a similar arrangement to the 747-400. The latest Honeywell FCC software, P/N 2216-HNP-03B-10 OPS (known as “-710” software) - Aug 2007 Its features include: Added the capability to arm VNAV prior to selection of Takeoff when compatible CDS and FMC part numbers are also installed. When armed, pitch takeoff will transition to VNAV engage at 400 feet. Note, due to inconsistencies associated with the arming of VNAV prior to takeoff, Boeing released the reference a) ops manual bulletin instructing flight crews to not attempt arming VNAV on the ground prior to takeoff. Added the capability to arm LNAV prior to selection of Takeoff when compatible CDS and FMC part numbers are installed. When armed, the takeoff roll mode will transition to LNAV engage at 50 feet. Revised design of “flight director only” LNAV ARM to LNAV ENG in roll go around to allow auto engagement of LNAV from Track Hold down to 50 feet whether the flight director switches are on or off. Note: This function is available as an option. This option is activated by incorporation of a negotiated Boeing Service Bulletin that will specify the correct FCC software, FMC software, CDS OPS and OPC software. Added logic to reduce false altitude acquires due to erroneous but un-flagged altitude inputs.

From line number 1278 onwards (Feb 2003) the Rockwell Collins enhanced MCP was introduced. This was designed to operate with the new Collins enhanced digital flight control system with integrates the autothrottle computer and Flight Control Computer (FCC) to enable Cat IIIb autoland. Note the Cat IIIb EDFCS has a rudder servo and can perform an engine out autoland. Most of the knobs have been redesigned and the buttons have the caption printed on them instead of on the panel. Notice the different angle of bank selector. There are Boeings comments upon how the new MCP was designed: "Collins provided a preliminary MCP design to Boeing in 2000 for Boeing pilots and airline pilots to evaluate in the simulator and comment on. Based upon those comments, a revised MCP was installed on a test 737NG in November 2001. Boeing test pilots evaluated that design for approximately 4 months. Based upon that evaluation, changes were made in the tactile, lighting and thermal characteristics to increase the similarity of the Collins and Honeywell MCPs. The goal during this evaluation was to make the Collins MCP operationally transparent to the flight crew when compared with the Honeywell MCP. Recent certification and service-ready testing has indicated that the latest Collins MCP has obtained a high level of crew transparency."   Flight Control Computer (FCC) The FCC is the brains of the Digital Flight Control System (DFCS) and like any other computer, its software is being improved (and debugged !) all the time. There are two identical FCC's in each aircraft and although either one is capable of managing all of the DFCS functions, both are required for Cat III autoland and autopilot go-around operation. The latest Collins FCC software, P/N 2275-COL-AC1-06 (known as “-150” or “P5.0” software) - Jun 2007 Its features include: Added changes in the application program associated with selection of the 737-900ER model pin (including a variable flare height). Removed a “pitch bump” which can occur when glide slope is captured from above. Eliminated the cause of a disconnect which may occur when flying dual channel autopilot go-arounds on the Alpha submode. Changed the ratcheted Radar Altimeter rate limit (used for ILS gain programming) from 21 to 50 feet per second to allow faster updating of rapid rises in approach terrain. Insured that an invalid minimum speed input disengages the VNAV mode or prevents entry into the VNAV mode.