Virgin 744 right wing gear stuck half up

[John H Watson]

Theory: As #4 hyd actuates both wing gear L & R, the final failure lies in the alternate right wing gear extension,

P.S. I say correct, but I don't know if crew procedures say that normal extension should be carried out first. As a result of low/no hydraulic pressure in the #4 system, perhaps this may have caused a partial and poorly sequenced normal extension which was unrecoverable (even using alternate extension).

[IefCooreman]

For info: the landing is indeed pretty hard for the case (not for a normal landing). Guidelines are to land as smoothly as possible, especially take care wings are level and make sure you can keep it on the runway. Then smoothly add speedbrakes if stopping distance is critical. Try to maintain wings level.

Why it is a hard landing? Only the guy himself knows that, but my impression is that many people forget the "human biology side" of these situations.  You end up reading books and chatting away with everybody, for hours and hours. It wears you down. Then when all decisions have been taken, you still have to do an unusual landing that is going to eat up a lot of runway... There is a sound level of stress involved, together with some 'tiredness'. You can see the nose being pulled up firmly the last second before touchdown.

My personal guess is he simply focussed too long on the touchdown point trying to make sure he was going to use as much runway as possible. Then looking at the end of the runway, you "notice" your flare is going to be a tad too late, your brain curses, and you try to avoid the hard touch by quickly "breaking" the descend rate. This might work on a 737, it doesn't on a heavy widebody. The bounce is logical since procedures require speedbrakes to remain unarmed. Now your brain curses all over the place, but it is what it is. You tried to do it too nice. Check and reset. When all is over, accept the comments from your collegues ("a good landing is one you can walk away from", blablabla), get a beer and now curse out aloud. Go home, stay away from the internet because the only thing everybody writes about... Right  :mrgreen:

The cabin is at "ease", they get the info that besides the annoying slight vibration, it is going to take a couple of hours and they can serve a meal etc if necessary to keep everybody calm. Serving alcohol... In view of a possible evacuation once on the ground it might not be a very wise decision.

[Will]

I think IefCooreman's suggestion sounds reasonable. Training and SOP would have them try to achieve as normal a landing as possible. I'm guessing that human factors got in the way, as opposed to an attempt to try a hard landing for some other tactical reason.

Las Vegas has massively long runways, so I don't think they'd be worried about trying an experimental technique to compensate for reduced braking. And I agree with John, that banging it down to try and free the gear is more likely to worsen the problem than to alleviate it.

Sometimes people will pull into a climb to try to use gravity (more properly: inertia) to overcome a stuck gear. But that would be done at a safe altitude.

[GodAtum]

The METAR:

METAR EGKK 291520Z 28006KT CAVOK 04/01 Q1040=
METAR EGKK 291550Z 31006KT CAVOK 04/01 Q1040=

[jonb]

Theory: As #4 hyd actuates both wing gear L & R, the final failure lies in the alternate right wing gear extension,

P.S. I say correct, but I don't know if crew procedures say that normal extension should be carried out first. As a result of low/no hydraulic pressure in the #4 system, perhaps this may have caused a partial and poorly sequenced normal extension which was unrecoverable (even using alternate extension).

The hyd press system 4 checklist calls for an alternate extension of both the nose/body and wing gear with the gear lever selected to off.,so no attempt at a normal extension. From there with a gear set not indicating down you would proceed to the gear disagree checklist.

[John H Watson]

Thanks, Jon

I'd be curious to know what caused the hydraulic failure in the first place which affected both the engine pump and demand pump. Perhaps a broken line which dumped all the hydraulic fluid.

[jonb]

You're wlecome John.
It would have to be something along those lines to cause a complete system loss yes.
I'm afraid I can't speculate too much as I fly for the company involved and we've been told, quite rightly, not to speculate or comment publicly on the incident.Though I can honestly say thus far I don't know anything more than has been written in the press anyway.
All the best for the new year.

[John H Watson]

Cheers, Jon.

This recent real world gear extension problem has raised some (non-procedural) "what-ifs".

What we are speculating: In that situation, the #4 hydraulic system was probably showing zero pressure and perhaps an empty reservior. I believe the crew would, by procedure, switch off the pumps manually to prevent damage to the pumps. They would extend all the gear using the Alternate Switches and they would be left in that position for landing.

Someone raised the question, what if the airport had fogged in, and it was necessary to fly to a distant alternate airport. A tech sim instructor (I believe) said it would be possible to retract the good gear, to reduce drag, by deslecting only the corresponding Alternate gear switch and putting the gear lever to UP using the functioning hydraulic system.  


Hypothetically, though, can landing gear be re-stowed using hydraulic power and the gear lever in UP if the Alternate system is still selected on? And what happens if the gear is subsequently selected to OFF.

Selecting the Alternate Gear Extension system makes the system run through a 40(?) second cycle (on later and modified aircraft it is forced to run through a full cycle, no matter how long the Alternate Switches are selected... Although, from memory, the switches have to be in the ON position for at least a second or two). A full cycle puts the motor actuator/cables back into a semi-normal state, but I'm not sure if it returns the hydraulic bypass valve back to normal. I also don't know if this new timer circuit prevents a subsequent alternate extension unless the switches are cycled.

(EDIT) Just had a look at the schematics. There is not a timer as such, but the circuit remains powered (even if the switch is deselected) via a PSEU (air/ground computer) "all gear downlocked" signal. The actuator motor is allowed to run though a complete cycle, whereupon an internal limit switch deactivates the motor.

Any gear experts out there?  :mrgreen:

[Sylle]

Very interesting to read all the tech talk here. Thanks guys!

On a sidenote... jonb - It would be great if you could confirm if the 3 Virgin Atlantic aircraft in PSX feature the correct customer options (equipment, callouts, etc).

Thanks in advance!
Cheers,
Sylvain

[Britjet]

I'm not entirely sure that it WAS a hard landing :-)
As has been said earlier, extending speedbrakes manually after touchdown is an that can enable the pilot to maintain roll control on the wings and prevent the aircraft rolling onto the gear fault side. If you land one of these things without speedbrake it is quite easy to "bounce" it! You certainly wouldn't thump it in to try and force the gear down. (That would be an office visit without biscuits...)

The loss of and outboard elevator if it was a hydraulic failure not prevent a smooth touchdown in itself, but I guess you never know..

Braking would be eroded but only by 25% or so (obviously) but Gatwick isn't the longest runway in the world for a 747 and I am sure that a landing over MLW would never have been an option. No need for it.

Just a few thoughts. I would be interested in how this failure manifested itself in the cruise...

Brit

[jonb]

On a sidenote... jonb - It would be great if you could confirm if the 3 Virgin Atlantic aircraft in PSX feature the correct customer options (equipment, callouts, etc).

Thanks in advance!
Cheers,
Sylvain

Hi Sylvain, I'm afraid to say I don't have a copy of PSX so I can't confirm it for you. I did the Virgin options file for HH back in the old days of PS1.3 so I'm sure Hardy has carried that config over and it's still correct. I've not been involved in this latest version apart from answering a couple of technical questions, and gathering some observations and bits of information(auto tuning etc) a couple of years back while it was still under development. ( did the weather  radar spikes from being scanned by military radar ever make it into the release?)
I was a tester/ technical adviser for the PMDG 744 but since then marriage and 2 small kids has meant I don't get the time for simming anymore and now my sim rig won't even turn on! I just occasionally pass by these forums to see how Hardy's project is/was coming along. (very well by the look of it!)
All the best.
Jon

[Jeroen Hoppenbrouwers]

(did the weather  radar spikes from being scanned by military radar ever make it into the release?)

You bet. We just don't tell where   :mrgreen:


Hoppie

[John H Watson]

Hypothetically, though, can landing gear be re-stowed using hydraulic power and the gear lever in UP if the Alternate system is still selected on? And what happens if the gear is subsequently selected to OFF.

According to one PPRuNer, if the alternate extension is completed and hydraulics are restored, the gear lever can be used normally (UP/OFF/DN). The Alternate switches are ignored (system-wise) until they are cycled OFF and back ON again.

Rgds
JHW

[Hardy Heinlin]

Would antiskid reduce the braking force on the good gear to avoid an excessive yaw moment? The wheels on the bad gear obviously won't rotate.

I assume braking on the good gear is still possible, even if it destabilizes the yaw control. Otherwise, when both gear on the same side were up, there was no braking at all. (In PSX, in this case, the aircraft yaws toward the good gear until the opposite wing tip touches the grass; at that point it yaws towards the grass.)


Cheers,

|-|ardy

[John H Watson]

Would antiskid reduce the braking force on the good gear to avoid an excessive yaw moment?

The antiskid system can only compare the braking of wheels on individual bogies (bogeys?). There is no comparison between bogies.

I assume that there would be more than normal weight on the remaining good gear on the right hand side (in the Virgin incident). Will more weight equal more grip? Or will that extra grip be too much and will the antiskid system cut in more often (putting the braking effect back to normal or less (for an individual bogey))

[Sylle]

Hi Sylvain, I'm afraid to say I don't have a copy of PSX so I can't confirm it for you. I did the Virgin options file for HH back in the old days of PS1.3 so I'm sure Hardy has carried that config over and it's still correct.

Thanks a lot Jon!
As Virgin didn't change the options over the years all should be good

Cheers,
Sylvain

[John H Watson]

There are rumours that an actuator was incorrectly installed prior to this incident. The Maintenance Manual installation procedures may have been deficient, however.

Rgds
JHW