View Full Version : B737 TECHNICAL QUESTIONS

25th Oct 2015, 11:01
Hi guys,

Some questions about the 737:

1: Can somebody tell me why shimmy dampers have been installed? Is that why the aircraft is "crabing" when it is on te ground?

2: In the event of a Fire detector fault, how can you define which engine loops are faulty?

Thank you

25th Oct 2015, 15:46
Raptor - I suggest you get your hands on FCOM 2 technical manual to answer your questions.

25th Oct 2015, 20:09
1. To stop the nose wheel trying to break itself by going to the disco as you try to keep the a/c on the black stuff.
1a. asked an answered years ago; so click on 'search'.
2. Review Fire Test in SP's.

25th Oct 2015, 20:10
There is a step-by-step procedure to determine the inoperative fire detection loop in FCOM.

25th Oct 2015, 21:51
After 13 years on 737s various, NO FCOM which I ever read, explained the taxy crabbing.

1 day, when I was awake, doing the walkaround, I noticed the dampers on the torque links and limited castoring ability of the MLGs and realised this was how the 'frame could accept a touchdown in autoland 15kts X-wind without "squeezing"the drift off.

NONE of the TRIs/TREs of any of the UK regulated companies for whom I worked could answer the question and when l pointed it out to them subsequently, they looked suitably sheepish and surprised a G O F like me had reasoned it out. :rolleyes:

Not one single Boeing/Company publication mentioned this mechanism on the 737 MLGs.

Hence the ability to taxy whilst pointing in a different direction!

Try pushing a supermarket trolley at speed and you'll soon realise the need for dampers on the NLG?

25th Oct 2015, 22:45
BM: I read your thoughts, but....I've always noticed B737's seem to be pointing right and taxying straight. X-winds come from both sides on an autoland, so I'm missing something in making the same connection; assuming yours is a technically serious solution.

25th Oct 2015, 23:23
dampers on the NLG?
I assume you mean the internal
modulating valve ??

26th Oct 2015, 00:26
Shimmy dampers on the NG are there to stop MLG shimmy. MLG shimmy is bad. We are talking ceiling panels falling down bad. After a lot of those events when the NG came (look mummy, no dampers!), Boeing decided to put the dampers back on the aircraft.
Fire loops? A and B. Test each one. The one that fails is faulty.

de facto
26th Oct 2015, 07:15
:EFire loops? A and B. Test each one. The one that fails is faulty.
clue:the nose points left in the southern hemisphere.:E

26th Oct 2015, 09:49
The guy who designed the undercarriage obviously had a labrador. They too crab walk nose to the right. It made him feel at home with his new pet.

26th Oct 2015, 11:35
The NG does't crab much. The classics do.

de facto
26th Oct 2015, 12:07
And crabs even more...regardless of wind.

Capt. Inop
26th Oct 2015, 21:23
MLG shimmy is bad. We are talking ceiling panels falling down bad.

Yeah. Once had the upper torque link go bonkers during rollout.
It was violent, and the cabin was a mess.

29th Oct 2015, 22:50
Have a lateral pull/push at the torque links on the NLG as you do the walkround. Any play, either at the "knee" joint or at the upper and/or lower phosphor bronze bushes will warn you your classic and NG is going to rattle on taxy, start to finish. Very often manifests itself as loud vibration just after liftoff, only ceasing when the NLG tyes rub the snubbers in the bay and stop rotation.

Take a look at the MLG "knee" joints. They are not bolted tightly together as per the NLG links (wear excepted) but you may see the efisculated (shiny) section of the NLG shimmy damper, depending on where it came to rest on parking.

Then look hard in the Boeing FCOM and waste some time looking for a reference to the MLG dampers. Unless of course they've since decided to inform their pilots of this since I hung my headset up.................

However, as I said in a previous posting, your F/O will be happier to know that the 'frame will take care of the first 15kts of the landing crosswind and he/she/it only has to cope with the remainder of the X-wind component?!

I promise to get out more............:)

Chesty Morgan
29th Oct 2015, 23:42
Had to google efisculated and it came up with emasculated. :ooh:

Fescalised is what you meant ;)

30th Oct 2015, 18:22
"Had to google efisculated and it came up with emasculated. :ooh:

Fescalised is what you meant ;)"

Serves me right for using big words!!

I should have said "the shiny bit which looks like a hydraulic ram".

After a few years in airline world maybe that's how we end up, emasculated??

Krystal n chips
30th Oct 2015, 18:48
You might also wish to consider uneven tyre wear and / or incorrect nose wheel px with regard to shimmy, not simply worn bushes, relevant though they are.

31st Oct 2015, 00:25
Download Boeing AERO 2013 Q3, theres a nice article about MLG shimmy.

13th Jan 2016, 08:57
About the partial or all gear up landing, why is the use of speed brakes not recommended?
Also, why in the event of Hyd Sys B failure, a flaps 15 landing is recommended? ( too much stress on the electric motor extending the flaps if going for flaps 30?)

Thank you

13th Jan 2016, 10:45
1. I think the friction coefficient between fuselage, engine nacelle and runway surface is sufficient to stop the aircraft within a normal runway's length without speedbrakes.

2. The alternate flaps system is VERY slow (0-40 is about 2 mins 30 sec). Not really nice if you get an engine failure somewhere along...

13th Jan 2016, 12:29
TCAS TA only.

It is a recommendation that anytime the a/c has a significant performance degradation the TCAS should be TA only. There are a variety of scenarios which would require this. Not all are mentioned in QRH and require airmanship. In some scenarios this selection appears quite early in the QRH list of actions, good idea.
However, in Engine failure case it is No.8 and takes quite a while to reach it. In the sim I timed it at nearly 2 minutes with some slow cadets. ANC is good. QRH comers under C and thus the start of the QRH can be after some time.
In Eng Fire/SEV DAM/SEP it is No. 12. It takes an absolute age to select TA Only, all the while you have lost 50% thrust and can not follow an RA.
Worse; in Volcanic Ash = close both T.Ls and no mention of TA Only. High Oil Temp, Low Oil Pressure no mention of TA only but 1 engine is at reduced thrust.

This is very inconsistent on the one hand, and when mentioned it is far too late. Just imagine what is happening in the cockpit during a high level engine failure. High work activity with procedures and ATC. (perhaps non radar), then in the middle you get a level off or even climb RA. What are you going to do? No choice, but can you comply. Surely you need to broadcast to all a/c ASAP that you are a wounded bird and tell them to get put of the way. TA only should almost be first action. It could save your neck and many others.

How can it be that some QRHs involving lost of thrust include TA Only and other do not?

13th Jan 2016, 13:04
Sorry RAT5, but I disagree with you.

An RA is NOT a common occurence, and the QRH in case of engine failures or issues correctly focusses first on SECURING the Aircraft and systems.

Only then, when time permits, shall we think about secondary consequences, like TA, fuel balancing and further intentions.
It is all about priorities, and selecting TA ( and 7700 by the way while securing the aircraft) is NOT.

13th Jan 2016, 14:02
An RA is NOT a common occurence, and the QRH in case of engine failures or issues correctly focusses first on SECURING the Aircraft and systems.

Neither is an engine failure, but I think we shall agree to disagreed on the issue. I thought securing the a/c involved all aspects of safety and avoiding an RA which you can not comply with IMHO fits neatly into that category. The 2 seconds it takes to move one switch 1 click to avoid a whole plethora of panic in an unpredictable future seems, for a professional operator, a minute distraction. Securing the engine is not a rushed action. PF is doing the A.N. bit and PM can twiddle a little knob.
There was an occurrence at hight FL. at night, where the crew had an engine failure. They forgot the basic A.N.C. and went straight for Engine Failure procedure. Good old simulator check ride stuff. After a very very short time, while they will still trying to figure out exactly what was happening, they got the stick shaker warning. They are now in RVSM with a SE stall recovery manoeuvre. Imagine if they then received an RA restricting their descent. Who here would ignore it or try, in vain, to comply. One little knob twiddled one little click would avoid that.

I do not have stats, but I suspect there are more RA's worldwide than engine failures. All I want to do is ensure the best chance of a safe outcome.

Chesty Morgan
13th Jan 2016, 16:16
Unless you are a dog owned by Pavlov then you probably won't react to an RA whilst in the middle of an engine failure.

If you blindly follow an RA without any thought then I suggest you should stay on the ground.

13th Jan 2016, 16:17
RAT5 if you want a good outcome just follow the QRH and company SOPs, its that simple. Don't you think Mr Boeing has already thought of that?

If you want RAT, after the memory items are completed, change the TCAS to TA only. The QRH does give the caveat of "The PIC can do any checklist off by memory if he feels that it will not jeopardise safety in doing so..."

13th Jan 2016, 23:29
Question about the


"Roll may be the result of trading edge flaps displacement due to a flap spindle fracture"

Is it possible to retract to flaps 1 in that case? Why a flaps 1 landing?

"Do not deploy speedbrakes in flight" why? Increase of vibrations I guess...


Why is a Flaps 15 landing recommanded in that situation?

14th Jan 2016, 06:44
TCAS RA is not a real problem, even according to Eurocontrol bulletins, is important that you don't maneuver against the RA, if you can't comply just stay where you are; and don't forget that in many cases, during any non normal checklist the crew gives a quick shout to the atc about the problem followed by the classic "standby".