b737 QRH -landing gear

[alexban]

Hy fellas
Can anybody explain me this:
In 737-efis QRH ,at' landing gear lever jammed in the up position' says: '.... total fuel quantity ..check
The following checklist should not be accomplished with less than 3800 kgs of total fuel quantity available.Land with gear up or land with any available gear if less than 3,800 kgs total fuel quantity is available.'
So,if you have more than 3800 kg fuel you could follow the checklist and extend manually the landing gear.
If you have less,you should belly-land the plane.
My obvious question is where did the 3800 kgs come from,what could be the reason for this quantity, if technical or practical reason?


And something of a different nature: on some of the instruments and pannels from the cockpit there is a small "+" .Does anybody know why is there,any technical reason?
thks
:ok:

[Right Way Up]

If part of the overhead panel is not illuminated when it should be, by pressing the + marks nearby you can re-light it. I have always assumed that the 3800 kgs part of that checklist is a time constraint, as it is a time consuming checklist. I also would like a definite answer.

[QAVION]

"And something of a different nature: on some of the instruments and panels from the cockpit there is a small "+" ."

Behind the + is a gold-plated electrical contact (a pin and socket arrangement) which electrically links the faceplate containing the lightbulbs with the mounting plate electrical supply. If the faceplate is loose, or the contact dirty, pushing/tapping on this point may reestablish electrical continuity (i.e. temporarily, until the engineers can clean the contacts, tighten the faceplate, replace the panel, etc).

Cheers.
Q.

[aviatorpk]

LANDING GEAR LEVER JAMMED IN UP POSITION
Checklist assumes that gear transfer valve has failed in Up or pressurized position Manual gear extension will not work A min. fuel is specified to emphasize that gear up is preferable to running out of fuel while trying to solve a gear problem:{

[alexban]

aiatorpk : ' Checklist assumes that gear transfer valve has failed in Up or pressurized position Manual gear extension will not work A min'...

Indeed the sistem remains pressurized,but if you follow the qrh,you should select sys A on stby rudder,then ,by cycling the speed brakes,you'll depressurize the sys A,to less than 500 psi. After that, you can use the manual landing gear extension handles. You must continue to use the speed brakes to relieve the pressure generated by the landing gear extension.All this will take no more than 15 min (~4 min/ldg gear).I suppose you should visually verify gear locked,so another 5 min.Make it 30 min--around 1000 kg fuel.No risk of remaining without fuel.
So my question is why 3800 kg fuel,exactly?
thks :hmm:
Alex

[FlyinWithoutWings]

Maybe the 3800kgs figure has to do with holding time available to you you with gear extended, as some gear will be already extended while the other extend.

B737-400 QRH, Performance Inflight Page PI.15.4- Fuel Flow per Engine per hour (at close to max take off weight 62000 kgs aprox) is 1910 kgs. Thats a total fuel requirement 3820 kgs for one hour of gear down holding. If you'll need say half an hour to carry out the checklist, the 3800kgs will ensure sufficient fuel for your approach as well.

IMHO :ok:

[mono]

My supposition (and it is just that) Is that this is the min fuel required for sufficient hydraulic cooling as this is the only relationship between fuel and hydraulics. A quick look at the MM states that the a/c electric pumps should not be run with less than approx 750kgs of fuel in each tank. However it is also stated that for gear retractions an external rig should be used as the ACMP's can't supply the demand (flow rate too low and possibility of an overheat).

A look at he QRH for gear lever jammed in up appears to show a heavy workload for not just the crew, but also the a/c pumps too in order to bleed off the constantly rising pressure as the gear is lowered.

The last thing you would want is to have to deal with a hydraulic o/heat QRH as well as attempting a gear freefall!!:\

Still just an opinion though

:ok:

[Taking Over, Nigel]

It's definitely a time/fuel constraint. Very lengthy proceedure.
Better to land gear up than run out of fuel.
You have to pick some figure- hence the 3800 - can't say "approx" in a checklist for legal reasons.
Me personally- 3700 kgs I'd do the checklist.

[CaptainSandL]

Our tech dept asked Boeing this very question several years ago this was their reply:

"A fuel quantity of 3800 kg was determined to provide adequate fuel reserves to complete the "LANDING GEAR LEVER JAMMED IN THE UP POSITION" checklist, lower the gear and verify all landing gear are down and locked, complete an approach to land, go-around with all landing gear in the extend position, and still have sufficient fuel available to land."

Pity they didn't explain that in the manuals somewhere rather than have us all guessing!



S & L (http://www.b737.org.uk)

[alexban]

Thks captainSandl.
So flyingwithoutwings was right.I also thought so,but it's not something to guess about.
:hmm:
3800 out of the blue.:sad:
:ok: