Virgin landing gear incident LGW!

[MarkerInbound]

Genuine question from a non-aviator, having just landed safely at 150kts or whatever the speed was, why is it deemed unsafe to slowly taxi the aircraft far enough clear of the runway so the airport can remain open?

The Boeing QRH has a "Caution" note in the landing gear checklists not to taxi the airplane or use the tiller if you have landed without all the landing gear down. "Caution" notes imply you can damage the aircraft if you don't follow them.

[dns]

Bump! Sorry to repost my earlier message but really curious about this one:

"Never flown heavy jets so this may be a stupid question, but would the flight crew in this case have deliberately pumped fuel to the left wing tanks in order to shift the centre of gravity and reduce the chances of a strike on a right engine during landing?"

[Oakape]

"Never flown heavy jets so this may be a stupid question, but would the flight crew in this case have deliberately pumped fuel to the left wing tanks in order to shift the centre of gravity and reduce the chances of a strike on a right engine during landing?"

Short answer is No. You can't pump fuel from one tank to another.

[ETOPS]

But you can dump from one if you wish.

[JammedStab]

Originally Posted by NSEU

Is it normal procedure for the crew to attempt a normal extension first, then use alternate extension for the remaining unextended gear?

The procedure for a loss of #4 hydraulic system is to extend all Landing Gear using the alternate gear extension system. That means that the Nose and Body gear are extended using the alternate system(separate switch) even though they still have normal hydraulic pressure.

For both actions in the checklist, there is a note saying "Action is irreversible". But is it really irreversible for the system with the functioning hydraulic system(which in this case was the gear that worked properly). After all, the hydraulics for that system are still working.

[gordonroxburgh]

For a no4 hyd system loss, what's the procedure for the wing gears, if nose and body are alternate?

[MarkerInbound]

When you get to that point of the checklist it's:


Gear Lever -OFF
Make sure you're less than 270 knots
ALTN GEAR EXTEND WING Switch - ALTN
ALTN GEAR EXTEND NOSE/BODY switch - ALTN
When all the gear are down - Gear Lever Down

[NSEU]

For both actions in the checklist, there is a note saying "Action is irreversible". But is it really irreversible for the system with the functioning hydraulic system(which in this case was the gear that worked properly). After all, the hydraulics for that system are still working.

In theory, yes. Is it advisable? probably not. An attempt at normal retraction may do further damage. In this situation, there may have been enough #4 hydraulic system pressure to unlock the left wing gear downlocks, but not retract them. This might prevent that gear from relocking (with the assist of gravity) on re-extension.

The question I have is: should there be a visual inspection done of the aircraft before takeoff? Do the flight or ground crew have to look for such damage? Being as it is under the wing but still plenty of headroom it would have been visible for anybody looking for it.

Basic inspections are carried out during transits. If it was broken before (I'm not saying it was before or after), would it have been spotted? It involves looking into the wheel well. The inboard doors are closed at this point, so viewing this device involves climbing into a very greasy and potentially dangerous wheel well. The maintenance manual has a very long list of to-do's before climbing in there.

This "small clip" is actually quite large and robust and heavily covered in green grease for (intended) slipperiness. What damage you might have spotted during a walkaround is debatable. As always, inspections are dictated by the manufacturer and aviation authorities. For example, you don't need to tighten the bolts holding on the wings after every flight

Genuine question from a non-aviator, having just landed safely at 150kts or whatever the speed was, why is it deemed unsafe to slowly taxi the aircraft far enough clear of the runway so the airport can remain open?

The 747-400 braking system has two hydraulic systems as backups, assuming the rest of the aircraft has power (electrical, pneumatic, etc). The #4 Hydraulic system is particularly important, however, as it repressurises the emergency braking system (which is used for parking, too). Taxiing usually involves turning or accelerating/decelerating an aircraft. This might tip over the aircraft (depending on CG and the gears not extended). Also, the brakes/tyres might be excessively hot due to manual braking and only 3 gears doing the braking. It seems to me like a good idea to stop the aircraft and let the fire crews to assess the exterior damage.

[woodpecker]

"Never flown heavy jets so this may be a stupid question, but would the flight crew in this case have deliberately pumped fuel to the left wing tanks in order to shift the centre of gravity and reduce the chances of a strike on a right engine during landing?"

Not a stupid question "DNS" but there are other "problems" with reducing fuel in one wing by selective dumping/engine feeding/crossfeeding using the overhead fuel panel.

I am sure the 747 fuel system is basically the same as the 777 that I flew, that is the first fuel tank(s) to be used are those in the centre/body part of the aircraft. To take it out of the wings would increase the "bending moment" at the wing root with all that weight inboard rather than outboard in the wing tanks.

So if we look at the Virgin flight the loss of No.4 hyd system would have required, once a return became the "plan", to dump fuel down to reduce the a/c weight down to below the max landing weight. It was not until (earlier than normal during the approach I would suggest) the alternate gear selection was made. Up to this point the loss of No. 4 hyd system was no real problem. I presume what followed was a discontinued approach and then the excursion to the south coast for further reduction of the landing weight by dumping or (with all that extra drag of most of the gear down) simply flying a few racetracks while coming up with a revised plan.

Personally, having dropped the gear on the first approach (on the alternate system) I would have been very reluctant to select it up on the main system without discussion with "those who understand the implications" more than myself.

At this point, to answer your question, "DNS", as long as there were no problems with leaving too much fuel inboard (the bending moments problem) it would have been very simple to have, by pump/crossfeed selections, to have fed all four engines from the starboard wing tank, reverting to "normal" feeds for the approach.

Basing this on the 777 fuel system I wait to be shot down by those 747-400 drivers out there..

[FERetd]

Classic/-400 differences

Gordon Roxburgh Quote "For a no4 hyd system loss, what's the procedure for the wing gears, if nose and body are alternate?"

MarkerInbound "Quote "When you get to that point of the checklist it's:


Gear Lever -OFF
Make sure you're less than 270 knots
ALTN GEAR EXTEND WING Switch - ALTN
ALTN GEAR EXTEND NOSE/BODY switch - ALTN
When all the gear are down - Gear Lever Down "

I cannot speak for the -400, but for the Classic the procedure for a #4 hydraulic system loss was to extend the trailing edge flaps and the wing gear using the alternate means. The nose and body gear were extended normally, using the operating #1 hydraulic system.

An extract from a Classic QRH - I don't suppose that a -400 is very different - apart from the references to the F/E, of course..

If SYS 1 Or 4 Lost:
E TE ALT Flaps Arm Switch ........................................ARM
F Flap Lever ..............................................LANDING FLAP
E TE ALT Flaps ........................................EXTEND FLAPS
5 ON SCHEDULE
F Gear Lever ............................................................ ....OFF
C Airspeed ...............................................230 TO 250 KIAS

If SYS 1 Lost:
F Nose & Body ALT Gear
Extend Switches.................................................... ...ARM

If SYS 4 Lost:
F Wing ALT Gear Extend Switches .............................ARM

In Either Case When Gear Extension Required:
F Applicable ALT Gear
Extend Switches ........................................HOLD IN EXT
10 SEC THEN ARM

In All Cases At The Appropriate Time
F Gear Lever ............................................................ DOWN
E TE ALT Flaps..........................EXTEND ON SCHEDULE
· If HYD SYS 1 or 4 inoperative observe placard
160 KIAS while extending flaps from 25 to 30.

[bcgallacher]

Woodpecker - selecting up after dropping the gear on alternate would only have raised the body gear as #4 hyd.system was inop. As I stated in a previous post I have been involved with the same problem some years ago in Sharjah - it is not really a big deal,the crew made a normal landing without any damage to the aircraft and seemed to regard it as a relatively minor issue. The biggest problem was fixing it - there were no 747 capable jacks in Sharjah so we had to fly them from Germany.The other problem was the Emerati authority who really had not the vaguest idea on how to handle things so basically stopped us from doing anything unless they had personnel to witness what we were doing which slowed things up considerably.

[Cytherea]

Sparks....

I don't believe that the photo shows sparks at all - I believe that given the angle direction and height of the winter sun (very low, bright clear day and on the nose) this picture shows a reflection of the sun in tyre smoke...There was no damage to the aircraft and no tyres were burst therefore no sparks are possible....

[MarkerInbound]

FE, they have made some changes from the Classic. The complete checklist for a HYD PRESS SYS 1, 2, 3, 4 is


1. DEMAND PUMP selector (affected system) - ON
2. ENGINE PUMP switch (affected system) - OFF
3. Do not accomplish the following checklist - HYD PRESS ENG
4. Choose one:
HYD PRESS SYS message blanks: Continue normal operations. ....
HYD PRESS SYS message stays shown - Go to step 5
5.DEMAND PUMP selector (affected system) - OFF
6. There are three pages of what you've lost based on what system you've lost. For system 4 it lists;
Right outboard elevator inop - Pitch control is reduced
Outboard trailing edge flap hydraulic operation inop - Trailing edge flaps move in secondary mode. Secondary extension from flaps 1 to 5 requires approximately 4 minutes. During approach, allow extra time for flap extension.
Two inboard spoiler panels on each wing inop - Roll rate and spoiler capability are reduced.
Wing gear hydraulic extension and retraction inop - Alternate gear extension is needed.
System 4 normal brake source inop - system 1 and 2 alternate brake sources are available.
Autobrake inop - Manual braking is needed.
7. Recall switch - Push
8. Choose one:
Only one HYD PRESS SYS message is shown - Go to step 9
More than one HYD PRESS SYS message is shown - Land at the nearest suitable airport, blah, blah, blah and go to step 9.
9. Do not use autoland.


It's got it's own descent checklist and then splits again based on which system or systems are inop. For system 4 you go to All Other System Failure Conditions. It starts with the note again that the trailing edge flaps will be in secondary mode and take 4 minutes from 1 to 5 and not to accomplish the FLAPS PRIMARY checklist. It then goes to:


Alternate Gear Extension


Landing gear lever - OFF
Do not exceed the gear EXTEND limit speed (270/.82M)
There's a warning the action is irreversible
ALTN GEAR EXTEND WING switch - ALTN
There's a warning the action is irreversible
ALTN GEAR EXTEND NOSE/BODY switch - ALTN


Reduction of speed to below .60 Mach may be needed for the wing gear to lock down.
When all gear are down: Landing gear lever - DN

There's a note if System 4 is inop to extend the ground spoilers manually and slowly And then it goes to the landing checklist.

[FERetd]

Classic/-400 differences

Thank you MarkerInbound.

[Intruder]

It is indeed possible in the 744 to burn fuel out of virtually any choice of tanks, using the pumps and crossfeed valves. In this case, open all crossfeed valves and turn off the pumps in tanks 1 & 2. However, such a transfer/burnoff may not be in the standard checklist, and the pilots may or may not choose to do so.

[JammedStab]

[/QUOTE]Concerning, selecting a set of gear back up on the good system after having done an alternate gear extension according to the QRH where both gear are selected down with the Alternate Gear Extend Switches.[/QUOTE]

I had a sim instructor at one point that said if for example, #4 hydraulics had failed and all gear had been extended with the alternate system(uses two switches, one for each hydraulic system) as per the QRH, if the weather deteriorated and now you had to go to your alternate with little fuel remaining, you could deselect the single alternate Gear Extend switch that controls the three gear legs powered by #1 system and then select the gear handle up to retract the Nose and Body Gear powered by number 1 system resulting in less fuel burn to your alternate.

Or similar if the other hydraulic system had failed and such a scenario was encountered. I would guess that his scenario is based on hydraulics being completely cut off for the system that still has the Alternate extension switch connected or an assumption of no hydraulic fluid left on the failed system.

So, I guess a question would be....what exactly happens when an Alternate Gear Extend Switch is selected to Alternate?

[MrPeabody]

JammedStab,

Selecting the ALTN gear switch drives electric motors on a gear uplock release mechanism, this also drives a cable run which operates a landing gear door safety valve (this ports both sides of the door actuator to return) and mechanically releases the internal locks with the landing gear door actuator.

With the wing gear, the operation of the electric motors is sequenced by position switches such that the motor operates to the extent that the door is unlocked and the safety valve at return position; the motor stops until the door is open and the motor restarts to release the gear uplock to drop the gear. At the completion of the cycle the motor resets the position of the system so the door safety valve is no longer ported to return.

[NSEU]

SMOC answered the ''basics'' here, Jammed Stab.

http://www.pprune.org/rumours-news/5...ml#post8803661

I guess it depends on how deep you wish to go. Delving into Maintainance Manuals and Wiring Schematics might be a little excessive (I was banging my head against a wall on numerous occasions trying to understand them). Anyway, it might be a good idea to find out if your aircraft has the latest and greatest modifications (one being the addition of extra relays and an input from the PSEU to help prevent the premature deactivation of the Altn Ext System by deselecting the Altn Ext Switch/es too early).

As previously stated, the system has to run through a complete cycle. I've read in some manuals, that at least 90 seconds should be allowed before deselecting the Altn Ext switches (presumably on the older type system) to allow this complete cycle.

I was wondering what would happen if there was a sudden (and miraculous) restoration of Hydraulic System 4 with the respective Altn Gear switch still on and the gear lever in UP. Would the gear go up? Would the doors close or stay down? (i.e. does the full alternate cycle reposition the safety valves?) (EDIT: just noticed Mr Peabody's response)

[MrPeabody]

NSEU,

With ALTN selected and gear lever up, then restoration of hydraulics would cause the gear to go up; doors would be powered to open. System would be in its normal mechanical state therefore when the gear uplock operates to the lock position then the gear doors will close. The ALTN circuit is latched until the switch is positioned to normal (off).

[MrPeabody]

This photo shows the wing gear doors (inner and outer) without any damage. Is that a flight control lube cover wedged between the wheel and door?