ATA 32    Landing gear

1 - NLG steering tiller installation: Not too tight! 737-3/4/500 

2 - Tire inspection guide, for training purposes.  737-ALL 

3 - PSEU does not come on. 737-6/7/8/900

4 - Nosewheel tire scrubbing examples. 737-ALL

5 - NLG strut shim / spacer information. 737-6/7/8/900

6 - Anti skid fail with Box 1-4 message during Bite. 737-6/7/8/900

7 - Landing Gear handle will not go to up position until flaps are retracted. 737-6/7/8/900

8 - Anti-Skid light illuminated on takeoff, goes out at liftoff.  737-6/7/8/900

9 - Antiskid inop light on.  737-6/7/8/900

10 - Autobrake disarm light illuminates upon touchdown without crew applying brakes. 737-ALL

11 - Autobrake disarm light ON but AACU bite shows nil faults. 737-6/7/8/900

        1 - NLG steering tiller installation: Not too tight! 737-3/4/500

When installing a nose wheel steering wheel (tiller),  you must tighten the nut 50-75 lbs/in above the running torque of the nut, with a max of 375 lbs/in, acc AMM.  Sometimes this is can be too high, which can result in a complaint that the nosewheel steering will not return to neutral exactly. The wheel may be running against the sidewall and the wheel turning force could be too high. Try to tighten the nut just that way that the wheel is really free to move, and that is comes back to neutral very easy. Even a very little axial play of the wheel is the ideal way to make sure the system operates smoothly!  But remember always follow the AMM first. You can use this tip at your own risk if you still have problems afterwards. 

        3 - PSEU does not come on. 737-6/7/8/900 

If the PSEU Display does not turn on when you push the ON/OFF Switch on the PSEU BITE panel, check the Fwd Access Door Switch S196 Plunger mechanism for proper function. If you find the Plunger stuck at Door closed position or otherwise defective, take corrective action as necessary.

This Switch is a part of the power circuit for PSEU. Thanks to someone from SAS.

        5 - NLG strut shim / spacer information.  737-6/7/8/900

When you install the NLG lower strut on the aircraft, for example after accomplishment of SB 737-53-1227 (Nose Wheel Drag Brace and Trunnion Bushing Replacement), you have to use shims (or spacers as they are called) to get a desired clearance between the strut and the fuselage (its about 0.20 to 0.38 mm , check the AMM first!)

According the IPC you must use shims with p/n 162A0303-X (where the X is for the different thickness of the shims) as required. But it is not stated what thickness a certain dashnumber has. Not in the AMM or IPC. Therefore you may use this information about these shims and their thickness.

See the pictures with the table about the different shims available. Note that -7, -8 and -9 shims are thinner that the -1 thru -6 shims ! Also 2 pictures are added to show the new bushing and nut at the aft side, after mentioned SB is accomplished. Dragbrace bushings are not shown here but are modified as well in the same way.

        6 - Anti skid fail with Box 1-4 message during Bite. 737-6/7/8/900

Discrepancy:
Anti skid fail with Box 1-4 message during Bite

Possible Fix:
Bad anti skid valve

Tip:
There is a FIM task for this fault message, but in most of the cases seen so
far it ends up being a anti skid valve which you find by checking resistance per FIM 32-42
task 804,paragraph F. (c), 180-240 ohms

Reason/Explanation:
The FIM starts you out trying a Anti skid module and some other things before
it moves you on to checking the valves.

Applicable Reference:
FIM 32-42-Task 804

Thanks to Tom S. for his input !

        7 - Landing Gear handle will not go to up position until flaps are retracted. 737-6/7/8/900

Discrepancy:
Landing Gear handle will not go to up position (Gear will not come up) until flaps are retracted

Possible Fix:
Loose pin in ground burndy block GD662

Tip:
PSEU fault code 31-51001( Ground Spoiler Interlock valve close sensor). The FIM calls out
the S1050 sensor, and the Ground spoiler interlock cable to be checked.
One of the later steps tells you to check wiring, S1050 uses GD662-DC for it's common leg. If it
is a loose pin, continuity will check good, but will come loose in flight.
You may also get reports of takeoff warning horns in flight.

Reason/Explanation:
Ground GD662-DC is a Burndy block ground that is located under the Cabin center aisle
floorboard. About 4 or 5 windows back from the overwing exit, just above the wheel well. If
the pin is loose at this connection, the ground will check good with a meter and a megger, but will vibrate loose in flight. The best way to rule out this problem is to remove the floorboard and pull on the individual wires at this block looking for a wire that pulls out. To gain access to this burndy block you must peel back the carpet and remove the panel. This effort could help avoid an air turnback.

Applicable Reference:
WDM 31-53-11, FIM 32-61 Task 825

Thanks to Tom S. for his input !

        8 - Anti-Skid light illuminated on takeoff, goes out at liftoff.  737-6/7/8/900

Applicable Reference:
SDS 32-42-00-002, FIM 32-42 Task 803, SSM 32-41-11, 27-62-11, AMM 27-62-00-820-812

Discrepancy:
Anti-Skid light illuminated on takeoff, goes out at liftoff

Possible Fix:
Replace M162 Antiskid/Autobrake Control Unit, and M980 Auto Speed Brake Module

Tip:
For this problem check to see if Auto Speed Brake Control Circuit breaker is open (C440). (Anti-skid does not need this circuit breaker in to operate, it is more a indication of a shorted M980 unit).
Perform AMM 27-62-00, Speed Brake RTO Test and repeat it for each of the brake positions (LI LO RI RO). During this test, check to make sure all 4 of the blue lights on the Auto Speed Brake Module lights come on, and that the Auto speed brake actuator deploys when tested in all 4 positions.

Reason/Explanation:

During this problem the AACU had a fault recorded of " SP CO LI indicates the left inboard wheel speed switch control disagrees with output for more than 3 seconds". In this case it appears that the Auto Speed Brake Module had a internal short that caused the C440 Circuit Breaker to open. It appears as though that same short burned up the AACU when "The AACU sends signals to the auto speedbrake module when each wheel speed is more than 60 knots."

"The auto speedbrake module uses the wheel speed input to operate the auto speedbrake actuator during the RTO function" Since this unit was shorted the 28VDC being sent to the Auto speed brake module, disagreed with the output for more than 3 seconds as stated in the fault code. Which correspondence with the Anti-skid light coming on during takeoff role when the aircraft reaches 60 knots and RTO is enabled. It was only during the RTO test when the AACU was placed in the position that correspondence to the fault message that the speed brake actuator would not deploy.

Thanks to Tom S. for his input !

        9 - Antiskid inop light on.  737-6/7/8/900

Discrepancy:
Antiskid inop light on

Possible Fix:
R626, R628, R627 Relay's, Anti skid unit

Tip:
Place Auto brake switch to RTO, if Auto Brake fail light does not come on, the Anti skid unit is not bad it is only a indication problem. Go to J22 juntion box (located behind left forward nose wheel well panel) remove D40668P connector does anti skid fail light go out," if it does", go to J24 juntion box(right forward nose wheel well panel) and replace R626 relay. "If it does not" remove connector D40670P from J22, light should go out and you can replace either R628, or R627, if it still does not: chase wire W5156-0633-22 from J22 to P2 panel.

Reason/Explanation:
Autobrake needs Antiskid to operate, by taking Autobrake to on and not having a AB fault, this indicates the Antiskid Unit is not setting this fault so it should be a indication problem with the light circuit.

Applicable Reference:
WDM32-41-11, 91-01-05

Thanks to Tom S. for his input !

      10- Autobrake disarm light illuminates upon touchdown without crew applying brakes. 737-ALL

Discrepancy: Autobrake disarm light illuminates upon touchdown without crew applying brakes

Possible Fix: Brake pedal switch (S762 or S763)

Tip: To test for a possible short in the left or right brake pedal switches. Use a mulltimeter and check left and right brake pedal switches (S762 and S763) for continuity between pins 1 and 2 with brakes off. If there is continuity, replace defective switch. Tapping on the switch while testing may help locate intermittant switches.

Reason/Explanation: If one or both of the switches is shorted (has continuity without brakes applied). The Autobrake system assumes that the pilot is applying brakes and will disarm the autobrake system causing the disarm light to illuminate.

Applicable Reference:
WDM 32-42-11, 32-42-01

Thanks to Tom S. for his input !

        11 - Autobrake disarm light ON but AACU bite shows nil faults. 737-6/7/8/900

Autobrake disarm light ON but AACU bite shows nil faults : when you put autobrake selector to any position, autobrake disarm light is ON, but AACU bite shows nil faults. If this snag is hard on you can go for replacement of Autobrake selector panel located on P2-2 panel.

This panel contains a R1 relay which is not monitored by AACU.whenever the relay is latched in fault condition, autobrake disarm light comes on even without any system fault.
Thanks to Raghavendra for this input !

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