Ask The Pilot

[Must...Fly!]

Regardless of if you can or not, I would have thought if you were gliding the last thing you'd be thinking about is dumping - it takes a lot of time to dump a little fuel

 

[jb747]

With aircraft that have fuel dumping capability, can a dump be done without engine power? Can the RAT provide power for this? I am thinking of a scenario where all engines are out (volcano, bird strike or frozen oil coolers, etc) and you need to glide as far as possible to make a landing. Unlikely I know, but so are things that do happen. (like oxygen bottles blasting off!)

Thinking back to basic aerody here...but if memory serves correctly, you'll actually glide further at a heavier weight, but your descent time will be reduced. So, heavy is better range, worse endurance.

And back on the original...the only aircraft I've flown with a RAT is the 380 (the 767 RAT did not provide electrics). Output is extremely limited, and heavy draw items like fuel pumps are amongst the loads that are shed. So no, you won't be dumping.

 

[Major]

Accident: Ryanair B738 and American B763 at Barcelona on Apr 14th 2011, both aircraft departed despite ground collision and passenger complaints

What is the purpose of the stabilizer in flight, and in this particular incident would there have been any indication of the damage from the flight deck ?

 

[jb747]

Accident: Ryanair B738 and American B763 at Barcelona on Apr 14th 2011, both aircraft departed despite ground collision and passenger complaints

What is the purpose of the stabilizer in flight, and in this particular incident would there have been any indication of the damage from the flight deck ?

Interesting read. Assuming it's accurate, the lack of professionalism from the Ryanair people is astounding. It's not only their own aircraft that they placed at risk, but they placed the AA aircraft at extreme risk, for no reason at all.

The horizontal stabiliser provides a downwards force. If it were to fall off, the aircraft would pitch down, probably irrecoverably. Aircraft exist that don't have them, but they get the downwards force by simply having wings that extend far enough aft of the c of g that rear mounted control surfaces will be able to provide that force. Loss of a single elevator shouldn't be too dramatic.

The 767 (and other airliners) tail moves in two ways. The entire tail pivots for trim, and the rear part (the elevators) are moved to allow pilot or autopilot pitch inputs. It's worth noting that the trimming effect is way stronger than the elevator effect.

It's probably not all that surprising that the hit wasn't noticed...it wouldn't have to be all that violent. But, the Ryanair crew knew that they were in close proximity to the 767, so having been told that the hit occurred, they probably should not have been all that surprised. There are clearance lines on most taxiways, and there is no excuse for taxying past anything that extends over the clearance line. As you can imagine, as the jets get bigger, it's even more of a problem, but parking by feel is unacceptable in cars...way less so in an aircraft.

Back onto the aircraft design...the downward force of the tailplane has to be countered by the wing making extra lift, and that means extra drag as well. Logically, the trimming force could actually be in either direction, and it would be better if it were positive. To achieve that you need to change the shape of the airliners pretty dramatically. Basically, you need a canard design, in which the horizontal tail surfaces are moved to the front of the aircraft, and the wing moved further aft...actually the 60's puppet show Thunderbirds had some airliners that were pretty much exactly that design.

 

[tuppaware]

Just finished reading QF32 and was wondering with all the degradations in the electric systems on the A380 on that flight, how different would of the situation been on the B747 ?

I assume apart from because its not FBW aircraft your controls would of just been heavier ? Would a pilot face less time running through checklists on the systems to work out what was or wasnt working ?

I just got the picture a lot of time was spent by the FO running through checklists of multiple errors more so then trying to get a picture of the damage to the system.

 

[jb747]

Just finished reading QF32 and was wondering with all the degradations in the electric systems on the A380 on that flight, how different would of the situation been on the B747 ?

I assume apart from because its not FBW aircraft your controls would of just been heavier ? Would a pilot face less time running through checklists on the systems to work out what was or wasnt working ?

I just got the picture a lot of time was spent by the FO running through checklists of multiple errors more so then trying to get a picture of the damage to the system.

Matt (FO) was a pretty busy boy. I think it's fair to say that Airbus never envisaged a need to do that many checklists, and the system had trouble with some parts of it. In particular, there was a level of 'circular' checklisting going on. One item would tell you to do something, and the very next would either cancel that, or tell you the opposite. I know him quite well, and he's very professional, and very experienced. I can't begin to imagine just how overwhelmed a 'cadet' FO would be in the same circumstances (and yes, I know 'cadets' aren't in A380s, but many airlines have them in the smaller members of the family, and they could be every bit as demanding). Some/many checklist items would ultimately have to be either cancelled, or ignored. It's worth noting that at the start of the Boeing checklists, it specifically says that the checklists are for the management of single failures, and that complex or compounding emergencies may require mixing checklists, or even simply falling back to system knowledge, and making it up as you go.

It is very difficult to say how a 747 would have handled the same level of insult. The engines are FADEC, so it's not impossible that the same sort of mode degradation would have happened (though there's only one mode reversion, not two). Manual manipulation of the thrust levers is easier in the 747 (in part because it is done all the time). I don't think the 747 would have been so restrictive with regard to the fuel dump, though if the wing was electrically dead, it would still have been problematic. Loss of the single hydraulic system associated with #2 would have barely mattered (and it isn't associated with the landing gear at all). I don't think the 747 braking would have been affected at all. Leading edge devices would not have been available, but trailing edge should have been unaffected. There would have been a minor level of degradation of all flight controls, but it may not have even been noticeable.

Control laws wouldn't have changed ('cos the 747 doesn't have them). Control loading would be the same as usual, though perhaps with a little more input required for any given result. As the loads vary from aircraft to aircraft anyway, I'd expect the variation to fall within that minor load difference anyway.

I know that RdC is big fan of the Airbus, but I'm not convinced that an identical event on a 747 would have been as hard to handle. I don't think anyone will volunteer to test that for you though.

 

[simongr]

I know that RdC is big fan of the Airbus, but I'm not convinced that an identical event on a 747 would have been as hard to handle. I don't think anyone will volunteer to test that for you though.

I guess you can never compare incidents and their impacts on different aircraft given that the Pilot/Crew has a major affect on how the incident plays out. If there were cadets in the FO seat then it is highly likely that the safe outcome for QF32 may not have occurred.

 

[jb747]

I guess you can never compare incidents and their impacts on different aircraft given that the Pilot/Crew has a major affect on how the incident plays out. If there were cadets in the FO seat then it is highly likely that the safe outcome for QF32 may not have occurred.

Comparing any event, especially across types is probably just about futile. The same actual failure and physical damage on a 747 would not have resulted in the same systems loss, and coming up with a scenario that gives the same system loss, most likely requires different damage.

The crew is always a huge part of things. A decent crew can give a good outcome in pretty bad circumstances....and conversely, a poor (or even unbalanced (i.e. good captain, poor FO, or vice versa)) crew can give a lousy result with a minor (or even no) event. Back up a couple of posts and have a think about the possible outcome of the Ryanair/AA event.

Something else for you all to think about. A good crew member isn't necessarily always that way. Crews can be degraded quite dramatically by lack of sleep, in particular. Mistakes at the end of long overnight sectors are always more common than at more reasonable body clock times. Around the world right now, lots of regulatory agencies are coming up with crew fatigue rules that ignore all of the science, and are based purely on what is economically of benefit to the airlines. When the accidents happen, they'll simply be 'crew error', so it won't even come back to haunt them....

 

[mjt57]

JB, harking back to an older video on YT, it's one of the first A380 vids, dep. LHR on NBW. About a minute after achieving positive climb it sounded like someone said "V2". Would this be right? If so, isn't V2 the declaration that you have to go, regardless?

 

[jb747]

JB, harking back to an older video on YT, it's one of the first A380 vids, dep. LHR on NBW. About a minute after achieving positive climb it sounded like someone said "V2". Would this be right? If so, isn't V2 the declaration that you have to go, regardless?

V1 is the go/no go speed. V2 isn't announced. The comment is "AP2 on", "AP2". Autopilot 2.

Use of the autopilot is "highly recommended" departing London for noise monitoring reasons. Basically if you're about a gnat's nut off track, you'll get hit with a thousand pound fine. Much easier to explain to the boss if the system did it.....

 

[harvyk]

V1 is the go/no go speed. V2 isn't announced. The comment is "AP2 on", "AP2". Autopilot 2.

Use of the autopilot is "highly recommended" departing London for noise monitoring reasons. Basically if you're about a gnat's nut off track, you'll get hit with a thousand pound fine. Much easier to explain to the boss if the system did it.....

How often is it that the autopilot doesn't do exactly as expected (eg more sluggish than expected, or not quite on track etc)?

 

[jb747]

How often is it that the autopilot doesn't do exactly as expected (eg more sluggish than expected, or not quite on track etc)?

Quite rare. Of course, the autopilot can't fix your mistakes (in the 737 that crashed into the Med a couple of years ago, attempts were made to engage the autopilot after the pilots had lost control...that won't work). Basically the autopilot is slower and has less control authority that the pilots, BUT, it has a perfect attention span, so small, but constant, corrections keep them very much down the centre of the road.

Actually another rule of aviation...if the autopilot is going to get things wrong, it will always be at the worst time. For instance, it will behave perfectly throughout an automatic approach, but will drop the wing in flare (or perhaps forget to do so). It's always a surprise...they don't lead up to it.

 

[mjt57]

V1 is the go/no go speed. V2 isn't announced. The comment is "AP2 on", "AP2". Autopilot 2.

Oh, OK. My ears need reaming, I'd guess...

Much easier to explain to the boss if the system did it.....

Yes, of course. We adopt the same philosophy at work...

 

[richie9x]

During push back there is a man (engineer?) with a headset that is connected to the plane. He walks along side the plane during push back. I assume he is able to talk to the pilot via the headset. What exactly is he there for? Is it to provide a set eyes on the ground to ensure there are no obstacles at ground level during push back? Or to make sure the plane is operating as it should? To ensure that remove before flight tags have been removed?

 

[jb747]

During push back there is a man (engineer?) with a headset that is connected to the plane. He walks along side the plane during push back. I assume he is able to talk to the pilot via the headset. What exactly is he there for? Is it to provide a set eyes on the ground to ensure there are no obstacles at ground level during push back? Or to make sure the plane is operating as it should? To ensure that remove before flight tags have been removed?

He is an engineer. He's there for lots of things. He controls the push back, once we give approval. He's gives us eyes on the engines as they start (lots of things can happen during the start, and they aren't necessarily obvious in the coughpit). Some of the little things than go wrong as an aircraft is powered up can be resolved in discussion with them. Hopefully any 'flight tags' are already removed (with the exception on the nose gear steering lock out, which is removed after push).

 

[mjt57]

with the exception on the nose gear steering lock out, which is removed after push).

That reminds me.

In another conversation I think you said that in order to help the aircraft turn when taxying, the main bogies can pivot or slew, something like that? If so, then when during pushback the tug turns the aircraft around how do the bogies operate to facilitate this?

 

[jb747]

That reminds me.

In another conversation I think you said that in order to help the aircraft turn when taxying, the main bogies can pivot or slew, something like that? If so, then when during pushback the tug turns the aircraft around how do the bogies operate to facilitate this?

The mechanics of the push back is not something we worry about all that much...but, if I recall correctly, as the nose gear moves off centre, the #4 hydraulic system in the jumbo reacts by pivoting the entire body gear trucks in concert. A similar thing happens in the 380, except that electro hydraulic pumps power up specifically to move just the aft pair of wheels on the body.

Both aircraft can be despatched with the body gear steering u/s. In the 747 it makes quite a dramatic difference, not so much to manoeuvrability, but to the drag experienced in the turn. The 380 system isn't as capable in the first place, so you don't really notice its absence...mainly it exists just to limit the dragging damage to the rear tyres...with it on, it's about the same as a 747 with it turned off.

 

[harvyk]

Something which the "PMDG 747" does in flight sim, if the number 4 hydraulic system is not functioning for whatever reason, the emergency exits on the upper deck won't open (all other exits can still be opened).

On the real 747 do those exits actually require hydraulic pressure to operate (considering they flip upwards). If the exits are required and they do require hydraulic pressure to operate is there a "manual mode" so to speak which does not require hydraulic pressure. Or is this simply a bug in the game?

* (I believe it was hyd 4, it's been a little while since I'd played around with it)

 

[jb747]

Something which the "PMDG 747" does in flight sim, if the number 4 hydraulic system is not functioning for whatever reason, the emergency exits on the upper deck won't open (all other exits can still be opened).

On the real 747 do those exits actually require hydraulic pressure to operate (considering they flip upwards). If the exits are required and they do require hydraulic pressure to operate is there a "manual mode" so to speak which does not require hydraulic pressure. Or is this simply a bug in the game?

* (I believe it was hyd 4, it's been a little while since I'd played around with it)

When you think about it, there's never going to be hydraulic pressure available during an evacuation...the pilots shut down everything before calling it. So, no, the door does not need hydraulics. There are power assists on all of the doors, but they are operated by gas pressure from small bottles nearby. If an upper deck door does not open correctly, I don't think it can be used at all. The crew will declare it blocked and direct people away from it.

 

[mjt57]

The mechanics of the push back is not something we worry about all that much...but, if I recall correctly, as the nose gear moves off centre, the #4 hydraulic system in the jumbo reacts by pivoting the entire body gear trucks in concert. A similar thing happens in the 380, except that electro hydraulic pumps power up specifically to move just the aft pair of wheels on the body.

Thanks for the explanation. That'd make sense, whether the nosewheel is turned via rudder pedals/tiller or via the tug that'd operate the rear wheels...

The other day I watched a B-Double reverse into an unloading bay at work. The rear tyres were just about moving sideways, although not really. It just looked like it. Lots of squealing and tyre distortion happening.

And they had but a mere 20t or so on them...