737 Landing Gear Transfer Unit

[SR71]

There have been two threads (now closed?) on the forum about operating the LGTU after a loss of System A fluid:

http://www.pprune.org/forums/showthread.php?t=83769&highlight=landing+gear+transfer+unit

and

http://www.pprune.org/forums/showthread.php?t=232184&highlight=landing+gear+transfer+unit

Is the consensus that it is possible to raise the gear in this case by shutting down the No 1 such that N2 reduces below 56% (Classic) - idle N2 is ~63% so won't achieve the objective....

Is the consensus also that in the EIS equipped classic's, there is no No 1 N2 tacho circuit breaker to pull that will accomplish the same objective, and that even in non-EIS equipped 737's where there is a circuit breaker, pulling this will have no effect, as it is only concerned with the integral lighting to the unit?

Not that anyone is advocating pulling breakers....

Thanks.

[bacem]

the N2= 56% signal comes from generator-tachymeter installed on the accessory gear box of the engine N°1. You may pull all the circuit brakes of the plane; it will not help you. You have to climb to a safe altitude the shut down the engine ,raise the gear then restart the engine again.
By the way; I have a good question for you: the hyd engine driven pump N°1 solonoid is inop. By MEL you are authorised to go. After take off , during the after takeoff c/L you wantto position the landing gear lever to the Off position.
The lever is jammed in the up position. What do you have to do to extend the gear?

[SR71]

Absolutely no idea.

:\

I presume the inop solenoid means you are unable to de-pressurise System A (no MEL here at home), so at a guess, shut down number 1 (to stop System A EDP pressurising System A fluid), and carry out the checklist for Landing Gear Lever Jammed in the Up Position?

[blackmail]

hello bacern,
may i try to find the answer?
you must somehow find a way to get rid of A hydraulic pressure to be able to extend the landing gear by gravity. but how?
the famous & delicate solenoid to isolate hydraulic EDP n°1, is burned out, meaning as long as engine n°1 is operating you will have hydraulic pressure, regardless of the A hydr. EDP switch position & pushing the gear up(landing gear lever jammed in up position). so, to start with, switch off elec hydraulic A pump, then shut down engine n°1, but that's only half the solution as, because the landing gear lever is in the(jammed) up position, the landing gear tranfer valve opens & hydraulic B pressure now keeps the gear up. so switch off both B hydraulic pumps, but before doing that, it might be a good idea to go to sby rudder to keep the aeroplane straight. so, here you are, in manual reversion, on one engine. seems to me a very tricky & uncomfortable flight situation but at least you can gravity extend the landing gear & please, leave the manual gear access panel open(NG), so the landing gear will not retract when restarting engine n°1 & restoring normal hydraulic power.
thinking about all this & notwithstanding what the MEL says, i would insist the solenoid to be changed before accepting the aeroplane for flight. finally, all above is just a brain exercise & in reality, if it ever happens, careful analysis & use of NNormal checklist usage should be tried first. but the mr. boeing NNormal checklist, although very good, does not consider multiple failures at the same time, which doesn' t mean it can' t happen.
wonder if i got it somewhat right?

regards,
bm

[yachtno1]

I'll take your word for it ! :D

[SR71]

Blackmail,

I forgot about the LGTU.

:\

By way of clarification I have no schematics with me...

The checklist for the Landing Gear Jammed in the Up Position directs one to cycle the speedbrake to relieve System A pressure after System A pumps are turned off....presumably because check-valves in the system mean that system pressure at the LG, even though the relevant pumps are turned off, is still high.

Somehow you need to relieve this and return it to the reservoir?

Similarly, even if you turn System B pumps off, will this be enough to relieve the pressure at the LG?

Maybe you still need to cycle the speedbrakes (because outboard flight spoilers are powered by system B) to relieve system B pressure whilst manually extending the gear?

Like you say, presumably I need to make sure the gear is down and locked else when I power up No 1 again, the gear may retract?

Curiously....

[blackmail]

hello sr71,

indeed curiously,yes, it might indeed be necessary to bleed off residual pressure in the landing gear lines as some liquid is trapped in the circuit, also hydraulic fluid will be tranferred from one side to the other via the landing gear transfer valve.
rgrds, bm

[mustafagander]

How much pressure will an EDHP on a windmilling engine generate?

[bacem]

Solution:
- Flight Ctl A switch to Stby Rudder
- Electric Pump2 (A) OFF
- Shut down engine N°1
- Landing gear transfer unit C/Bs (there are 2) on P6 PULL
- Land with this configuration
- Don't use the alternate nose wheel steering.
-After landing immediately put the Pin in the nose landing gear (As soon as possible):ugh: :ugh:

[SR71]

Hmmm....

My book says Gear Sys XFer Valve on Classic is P6.2 D14/15, and on NG, P6.2 C15/16?

:confused:

I'll ask to try it in the sim...

:ok:

[blackmail]

sr71, bacern, mustafagander & others, hello,
i agree with both of you , i have also for the ng, the ldg gear tfr unit cb's on P6-2, C15 & C16.
although our sop's recommend not to pull cb's unless required by a NNormal procedure, i admit in this case, it would be better to first pull the relevant ldg gear tfr valve cb's, avoiding a momentary full manual reversion mode.
for the classics you need to land with the n°1 engine out, but on the NG, if you leave the manual landing gear access panel open , the landing gear will not retract by restarting the n°1 engine. also, what remaining hydraulic pressure, if any, a windmilling engine will produce, i don ' t know, but it' s a good question.
rgrds,
bm

[bacem]

Hi;
My mistake, CBs are on the P6 panel.that's correct.

[arba]

Hello BACEM,
Company MEL, only Syst B depressurization function may be inoperative , with
repair interval ten consecutive days.

May be they thought about it already.