View Full Version : B737 Nonnormal Cklist Trivia
Anybody able to explain why, in the LANDING GEAR LEVER JAMMED IN THE UP POSITION we are told to land with Flaps 15, and why not in the LOSS OF SYSTEM A ?
In both cases we loose sys A pressure.... :confused:
LEM
Seat1APlease
2nd Feb 2005, 22:25
I don't know which version you are referring to, but could it be that they are considering the go around situation.
If the lever is stuck in the up position then you can drop the gear using the free fall but in the event of a G/A you may not be able to retract it.
I once had a situation where the flaps didn't respond to normal selection and we elected to land with flaps 15. Our thinking was that even with gear down and flaps 15 you should still have enough thrust to do a G/A.
It is a bit late at night to give it further thought but perhaps that is a start.
regards.
Hi Seat1APlease,
the go around thing was the first that came to my mind, but actually, comparing the two cklists, it should be the opposite!
When you really loose system A, you really can't raise the gear - but they want us to land with full flaps.
When we purposely depressurize system A, we can always raise the gear in a go around, simply by turning back the Hyd pumps on - but they want us to land with flaps 15.
_______________________________________________
In electing to land with flaps 15 after a TRAILING EDGE FLAPS DISAGREE situation, you exactly did what the cklist says, using Alternate Flaps Extension.
Keep the posts coming!:ok:
ps: I'm talking classic.
When you really loose system A, you really can't raise the gear - unless you are STUCK for a gear down, in-range diversion, of course!
alexban
3rd Feb 2005, 18:39
Hy LEM :
My guess the explanation is this:
from the nnc 14.6 'ldg gear lever jammed in up position'....
' Set Vref 15 +10 kts.
[ Provides tail clearance during landing since hydraulic system A flight spoilers will be unlocked and may float] '
what happens is this: with ldg gear lever jammed in up position the hydraulic pressure is locked in system A,that's why you have to use the speed braake lever to relieve pressure from sys A in order to extend the ldg gear.
By doing this,you'll have no pressure in sys A,and the inboard flight spoilers will be not only inoperative,as in the other nn case-loss of press sys A-,but more important ,they'll be UNLOCKED,so a chance to deploy when landing,causing a tail strike.
That's the reason for flap 15 ldg in this case,not necessary though in the other case-loss of sys A-,where the flight spoilers will remain inoperative but locked.
Then again,that's my guess,but I think I'm right.
Brgds Alex
HI BOAC, perhaps because I'm tired I really don't see what you mean :confused:
Hi Alex!
maybe I've missed something in the books...
Why the spoilers are unlocked if you purposely depressurize, and why not if you loose A pressure????
Anyway, I thought that larger flaps settings reduce the risk of tail strike, not the opposite...
:confused:
JABBARA
3rd Feb 2005, 22:46
Just an aerodynamic explanation (a guess):
The lift over the wing is created by a vacuum (negative pressure distrubution). This vacuum will suck the unlocked spoilers up and cause them to be floating. Eventually the created lift somehow will be destroyed. To maintain the desired lift, the AOA (during flare this can be commented as body attitude) should be increasead and consequently this may cause a tail strike.
The shape of the pressure distrubution ( vacuum) over the wing surface will be varying with AOA. Higher AOA at Flap 15 will make the the peak point of this vacuum shape close to leading edge as reducing the likelihood of this floating and so the tail strike as well.
alexban
4th Feb 2005, 07:05
Lem, if the sys A failes the pressure will be locked by check valves in the sys ,locking also the spoilers.
In order to release the gear,(in case of ldg gr lever jammed up ) you'll cycle the speed brake lever,releasing the pressure.
This will leave the spoilers unlocked.
Jabbara gave you the right answer concerning the aerodinamics of using flap 15, I guess.
That phrase I ve underlined in my previous answer it's in the Dec 3,2004 revision of the QRH.
Brgds
Alex
You are right , gentlemen!
Now I've got it, and I thank you very much for your help!
:ok: LEM
HI BOAC, perhaps because I'm tired I really don't see what you mean - it was suggested to me (years ago) by a 'wise old head' that shutting down No1 when conditions permit might allow the LGTU to raise the gear.