Ask The Pilot

[jb747]

Cool. Nice little fire risk with liquid I guess. But the advantage must be greater on board volume in gas form, I guess.

I doubt that the fire risk was any greater than it would be with pressurised oxygen. Handling it is a different matter. It went through a couple of pressure reduction phases before getting to the mask. It was a pure oxygen system, which always delivered 100% to the mask, without any ambient mixing. So very different to the gaseous systems in the military or civil worlds.

I was wondering about the qantas 747 where the oxygen bottle failed.

I know a bit about that event. What, specifically, do you want to know?

 

[747sp]

JB I do have a question about QF 30 . If the same event happen over Europe or North America, with a larger choice of airports in close proximity, what criteria would you use to pick the best place to land ?

 

[jb747]

JB I do have a question about QF 30 . If the same event happen over Europe or North America, with a larger choice of airports in close proximity, what criteria would you use to pick the best place to land ?

As we flew along, we always kept a mental map of the airports around you that you could use. Over Europe, and NA, large airports are always quite close, so you will pretty well invariably have a choice. In the case of QF30, weather would be an overriding consideration, as our ability to fly an instrument approach was compromised. We needed to hurry, but not rush. It took time to dump the fuel, and whilst that was absorbed by the flight to Manila, it means that a closer airport might not have had us on the ground any sooner. If all other things are equal, I'd go to an airport I was familiar with, rather than one I'd never been to.

 

[Vic]

I know a bit about that event. What, specifically, do you want to know?

It was just a general comment, as my impression was the incident involved a gas cylinder exploding and I thought it was part of the pax oxygen system. But sounds like it was for the pilots only.

BTW we got a B+ for the physics report. Disappointingly the teacher was not happy with bleed holes as a safety feature since they have not yet been taught about air pressures etc., but have only done forces, momentum, newton's laws, etc. So the safety feature in the final report was the seat belt - how boringly disappointing.

 

[jb747]

It was just a general comment, as my impression was the incident involved a gas cylinder exploding and I thought it was part of the pax oxygen system. But sounds like it was for the pilots only.

In the 747, there are two oxygen bottles dedicated to the coughpit. There are 13 other bottles for the cabin. these bottles are all identical, and are interchangeable. The bottle that went bang, had originally been delivered as a 767 coughpit bottle. The 767 used bottles for the coughpit and chemical generators for the cabin. During its life it had moved from the 767, to a 747-300, and then to two installations on the -400. When it failed it was #4 in a bank of 7 passenger bottles.

 

[JohnM]

When it failed it was #4 in a bank of 7 passenger bottles.

Could the event have been markedly nastier if that bottle had been in one of the other positions in that rack?

 

[Cheatah]

Could the event have been markedly nastier if that bottle had been in one of the other positions in that rack?

Or, if it happened during one of the Antarctic sightseeing flights!

 

[jb747]

Could the event have been markedly nastier if that bottle had been in one of the other positions in that rack?

Given that this failure could have happened in any bottle position, it is interesting to ponder the issues that would have arisen if the failure had been in a different spot.

For any bottle position in the rack of 7, I would expect the external, cabling, and wiring, damage to have been much the same. The damage inflicted by the 80% (or so) of the bottle that came into the cabin would have differed though. The worst bottle would have been #1, as that may have impacted one of the business class seats. #2 and #3 would have been much the same as we had, but they would not have hit the door handle. As that handle served to remove much of the energy from the bottle, either of those bottles may have made it to the upper deck. There's a cupboard there, but they may have had sufficient energy to exit the cabin. #4 we know. #5, 6, and probably 7, would have impacted the slide raft, which would have stopped them.

But, the worst possible situation would have been if the bottle failure had occurred in either of the crew positions. They are mounted horizontally, with the valve end pointed aft. The pressure would have blown out the fuselage, as happened, but the projectile damage would have been more dangerous, as it would have been pointed through the frames, and the passenger bottles were not far away. So, the worst case would have had it passing through a frame or two, and then impacting the #1 bottle.

Or, if it happened during one of the Antarctic sightseeing flights!

Probably not any more of an issue than mid ocean. All flights are planned with depressuration contingencies, which allow for the depressurisation to happen at the worst time. It would have been a cold, slow, long, flight back though.

 

[ayebee]

I did enjoy that place a lot.

reprising the Kai Tak discussion a few pages back.

Happened on this video

Some excellent historic pics and presented in a non-sensational style.

 

[RailFlyer]

Question for the pilots. Is it surprising that the crew of PIA8303 didn't cause more damage to the bottom of the fuselage and/or rip the engines off the plane on their first attempt to land? If you are not aiming for the most greasy of landings and are expecting the landing gear suspension to handle the impact, do you not normally hit the runway with enough force to cause some major damage? From the pictures of the plane before it crashed the damage doesn't look much worse than abrasions/minor damage on the bottom of the engine cowlings and it seems the engines were intact enough to continue operating for a few minutes after the collision with the runway, before at least their gearboxes failed.

Are you taught what to expect if you had to land without landing gear? Would you expect engines still to be attached to the wings and mostly intact? Or would you expect major, obvious damage and even structural failure? (and obviously that would be when you are expecting to land softly without any wheels!)

 

[jb747]

Question for the pilots. Is it surprising that the crew of PIA8303 didn't cause more damage to the bottom of the fuselage and/or rip the engines off the plane on their first attempt to land? If you are not aiming for the most greasy of landings and are expecting the landing gear suspension to handle the impact, do you not normally hit the runway with enough force to cause some major damage? From the pictures of the plane before it crashed the damage doesn't look much worse than abrasions/minor damage on the bottom of the engine cowlings and it seems the engines were intact enough to continue operating for a few minutes after the collision with the runway, before at least their gearboxes failed.

Whilst I never chased greasers, smooth was always nice if it happened.

From what I gather this aircraft was travelling much faster than normal, that would mean that the wings would be producing more lift for a given pitch attitude. To actually make it sit down, with any substantial weight on the engines, you'd probably have to push forward a bit. The spoilers, which function to kill the lift in a normal landing, would not have functioned here, as they are activated by weight on the wheels. The upshot would be that most of the weight would still be borne by the wings.

I would expect the damage to rapidly increase with any substantial weight on the pylons. But, I can't quantify what would qualify as substantial.

Are you taught what to expect if you had to land without landing gear? Would you expect engines still to be attached to the wings and mostly intact? Or would you expect major, obvious damage and even structural failure? (and obviously that would be when you are expecting to land softly without any wheels!)

It's never a practice item, though it is discussed in the various manuals. I would expect to shed the engines.

 

[AviatorInsight]

Question for the pilots. Is it surprising that the crew of PIA8303 didn't cause more damage to the bottom of the fuselage and/or rip the engines off the plane on their first attempt to land? If you are not aiming for the most greasy of landings and are expecting the landing gear suspension to handle the impact, do you not normally hit the runway with enough force to cause some major damage? From the pictures of the plane before it crashed the damage doesn't look much worse than abrasions/minor damage on the bottom of the engine cowlings and it seems the engines were intact enough to continue operating for a few minutes after the collision with the runway, before at least their gearboxes failed.

Are you taught what to expect if you had to land without landing gear? Would you expect engines still to be attached to the wings and mostly intact? Or would you expect major, obvious damage and even structural failure? (and obviously that would be when you are expecting to land softly without any wheels!)

When a fixed wing aircraft flies close to the ground, it encounters an effect known as ground effect. Without getting into the technical side of things (unless you want me to), this creates a “cushion” of air underneath the wings.

The lower/nearer the wing is with regards to the ground, the more pronounced the ground effect becomes. While in ground effect, the wing requires a lower angle of attack to produce the same amount of lift.

This produces a noticeable “floating” effect which makes sense as to why they touched down so far down the runway.

It’s also noticeable on normal flights with the 737 especially seeing as it sits much lower to the ground than the A320, it’s been given the nickname the “Boeing push”. Where the pilot will forcibly push the control column forward momentarily to break the ground effect and put the wheels on the ground.

 

[RailFlyer]

Thanks both. That makes sense, a combination of ground effect, lack of spoilers etc, leading to a floating with possibly minimal force onto the runway when it did bounce/scrape along.

So if you were in that scenario (no gear) but did know about it and did want to stop, obviously you would approach slower but what else could you do to prevent floating (jamming the nose down with no wheels doesn't seem intuitive), can you manual trigger the spoilers through an override?

 

[jb747]

Thanks both. That makes sense, a combination of ground effect, lack of spoilers etc, leading to a floating with possibly minimal force onto the runway when it did bounce/scrape along.

I haven't seen the exact speed at which he arrived at the runway, but at 500' he was at 220 knots. Almost 100 knots fast. I don't expect that he would have lost much, if any of that speed between 500' and 'touchdown'. So fast that it beggars belief.

So if you were in that scenario (no gear) but did know about it and did want to stop, obviously you would approach slower but what else could you do to prevent floating (jamming the nose down with no wheels doesn't seem intuitive), can you manual trigger the spoilers through an override?

If I wanted to do a gear up landing....I'd have the spoilers disarmed. APU running, and it's buses tied to the electrical system. Fly the approach as normally as possible, at the normal approach speeds. Full flap. As the thrust levers are taken to idle in the flare, FO to flick the fuel switches to cutoff, and immediately pull all of the fire handles. Manually select speed brake (which would give you a different array of panels and rise than you get with ground spoilers). Evacuation checklist immediately the aircraft stops. Run away.

 

[AviatorInsight]

If I wanted to do a gear up landing....I'd have the spoilers disarmed. APU running, and it's buses tied to the electrical system. Fly the approach as normally as possible, at the normal approach speeds. Full flap. As the thrust levers are taken to idle in the flare, FO to flick the fuel switches to cutoff, and immediately pull all of the fire handles. Manually select speed brake (which would give you a different array of panels and rise than you get with ground spoilers). Evacuation checklist immediately the aircraft stops. Run away.

Interesting. Is that your own thing or from the 380 checklist?

Here’s the 737 checklist for a gear up landing.
Flap 40 landing. Pull circuit breakers for Gear warning horn and auto speedbrake (this prevents inadvertent deployment of ground spoilers after landing). Do not arm speedbrakes.
Landing Review.
Do not extend speedbrakes unless stopping distance is critical. When distance is critical, extend the speedbrakes after all gear, nose or engine nacelle have contacted the runway. Do not use reversers unless distance is critical. Turn all fuel pumps off just before the flare. Do evacuation checklist if needed.

Additional items. APU OFF. When on approach, engine Bleed air switches OFF. This ensures aircraft is depressurised at touchdown.

 

[jb747]

Interesting. Is that your own thing or from the 380 checklist?

Off the top of my head. I don’t have access to the 380 manuals when I‘m on my iPad.

 

[jb747]

Now that I've looked at the manual...

There is no checklist for landing with all gear retracted. There are various permutations, but the thinking is obviously that as there are four main gear and multiple hydraulic systems involved, as well as gravity extension with a totally different electrical path, that the chances of you intentionally wanting to do this are effectively zero.

The closest is landing with two main gear out on the same side, and it's not substantially different to my guess. APU isn't mentioned, but I put it in to ensure the electrical supply (and therefore flight law) when the engines were shutting down. Selection of engine masters is as I suggested.

 

[OATEK]

Now that I've looked at the manual...

There is no checklist for landing with all gear retracted. There are various permutations, but the thinking is obviously that as there are four main gear and multiple hydraulic systems involved, as well as gravity extension with a totally different electrical path, that the chances of you intentionally wanting to do this are effectively zero.

The closest is landing with two main gear out on the same side, and it's not substantially different to my guess. APU isn't mentioned, but I put it in to ensure the electrical supply (and therefore flight law) when the engines were shutting down. Selection of engine masters is as I suggested.

Not even for a belly flop on water?

 

[jb747]

Not even for a belly flop on water?

Yes, there’s a ditching checklist, but the ultimate aim is a little different. I don‘t really want to land on operating engines, and fire is going to be the biggest immediate concern. Landing on water, the engines will self extinguish immediately.

Most ditching scenarios are just to make you feel good. I would have zero confidence in the outcome of a deep ocean ditching in a large airliner. And at night...no chance. An enclosed, calm, bit of water (i.e. the Hudson), during daylight, is somewhat different.

 

[RailFlyer]

Most ditching scenarios are just to make you feel good. I would have zero confidence in the outcome of a deep ocean ditching in a large airliner. And at night...no chance. An enclosed, calm, bit of water (i.e. the Hudson), during daylight, is somewhat different.

Did you have any more faith in an ocean ditching in your A-4 or were you always taught to eject if that was inevitable? What about an unpowered landing on land away from an airport - i.e. using a long road?

Out of interest why does being at night make an ocean ditching so less likely to lead to a good outcome? Assuming you had a perfectly working aircraft (except for the engines), would the radio altimeter and other instruments not give you enough information to pull off a good enough flare and wings-level landing to make the contact with the water similar to day time, or do you need a lot more visual clues to get it perfect enough to have a chance? I would have thought waves were the biggest threat, regardless of time of day.