Ask The Pilot

[Warragul]

I wasn't inferring that the aircraft should have diverted to Kiribati, knowing nothing about what determines which location is selected. I just thought the video spent quite some time on why it was not suitable for this event.

 

[jb747]

There are degrees to any emergency. An engine shutdown (not a failure) is interesting, but not a desperate situation. You can fly for hours like this, and whilst you shouldn't fly past any decent airports (facilities and weather), you most certainly shouldn't make it worse by trying to throw it into a marginal field. At the other end of the scale, you have things that are bad enough to accept throwing the aircraft away...that's when you end up with a ditching, or landing at a totally unsuitable airport. In those cases, you have a great deal of risk to the passengers, so what's going on to make that the better of the options.

A cargo fire may be contained by the suppression system, but even if it does slow things down, you have a limited time frame for finding somewhere to land. It is probably one of the most dangerous situations....if it is confirmed. So, taking the Baku event, if any form of smoke or heat reaches the cabin, any runway, anywhere, would do...and that could progress to any flat bit of land or water. Off the top of my head, I can't think of any successful outcomes from actual hold fires. The number of engines is irrelevant to any fire within the fuselage.

There were a couple of spots in the Pacific that were basically just places you might ditch. Kiribati is one. Johnston Island is another.

 

[Captain Halliday]

In an extreme like a fire in the hold, would runways shorter than usual come into consideration?

In other words, might an overrun be preferable to ditching?

 

[justinbrett]

I wasn't inferring that the aircraft should have diverted to Kiribati, knowing nothing about what determines which location is selected. I just thought the video spent quite some time on why it was not suitable for this event.

It was less than 30 seconds - he was just explaining the thought process about how to select diverts and that not all diverts are equal.

I thought it was a very well explained video, sounds like he is ex USAF and I'm guessing was an instructor.

 

[Saab34]

What would be the fastest time you would be able to ditch should a cabin fire eventuate at say cruise height (like over the Pacific). Do you think you could get a A380 or 737 down in 5 mins? (Without it breaking apart on the way down)

 

[jb747]

In an extreme like a fire in the hold, would runways shorter than usual come into consideration?

In other words, might an overrun be preferable to ditching?

As long as it isn't fall off a cliff at the end of the runway.

What would be the fastest time you would be able to ditch should a cabin fire eventuate at say cruise height (like over the Pacific). Do you think you could get a A380 or 737 down in 5 mins? (Without it breaking apart on the way down)

Nope. About 7 minutes to get down. Then it would take another couple to lose the speed. And at least a couple more to find the ocean (assuming you don't want to just drive into it).

 

[Quickstatus]

find the ocean

How long did AF477 take to find the ocean.

Without it breaking apart on the way down

I recall AF477 did not breakup on the way down…

 

[jb747]

How long did AF477 take to find the ocean.

Two or three minutes. I refrained from pointing out that there are ways of getting to the bottom quicker, as they aren't actually survivable.

I recall AF477 did not breakup on the way down…

Irrelevant. And how many survived the arrival?

 

[Quickstatus]

Irrelevant

Except that even with the AF477 descent at a rate higher than one that increases survivability, the airframe remained intact.

There was one where a B747 went inverted and bits fell off. Air China or something looks that. But everyone survived. Can’t remember what flight number. Though the airframe may have been written off after doing the acrobatics

What would be the attitude of the aircraft if needing to do an emergency descent of a few minutes?

 

[Saab34]

Is ditching or these 7 minute descents something that is also done in sim training?

 

[Skiddy_au]

This video from a AA pilot gives a good rundown (for a non pilot person) on this. Although he seems to have a bee in his bonnet about Christmas Island - in Kiribati not the Indian Ocean.

I had no idea this guy was a professional pilot. I was religiously watching his videos around the the Oroville Dam spillway crisis. He seemed like a journalist, including asking questions at press conferences. He has a good grasp of crisis responses.

 

[jb747]

Except that even with the AF477 descent at a rate higher than one that increases survivability, the airframe remained intact.

I don't see the point. Yep, in a deep stall, or even a spin, the aircraft will descend really, really fast. Trouble is that it will still be going at that sink rate at the bottom.

There was one where a B747 went inverted and bits fell off. Air China or something looks that. But everyone survived. Can’t remember what flight number. Though the airframe may have been written off after doing the acrobatics.

There was a lot of luck in that. The failures occurred in the recovery, literally pulling enough G to break parts off the tail. Some very nasty things happen control and trim-wise if you go too fast.

What would be the attitude of the aircraft if needing to do an emergency descent of a few minutes?

Attitude? Not that steep. You'd have full speed brake, and Mmo into Vmo. Minus -5º perhaps.

Is ditching or these 7 minute descents something that is also done in sim training?

Rapid descents are part of the training for depressurisations. I've done the ditching checklist in the sim, but we got an engine back, and so avoided doing something wouldn't simulate well, and which would probably be negative training. Cargo fires involving rapid turn backs and landings immediately after take off come up every now and then.

 

[RooFlyer]

There was a lot of luck in that. The failures occurred in the recovery, literally pulling enough G to break parts off the tail. Some very nasty things happen control and trim-wise if you go too fast.

Then there was this case of a US Air Force Grissom KC-135E tanker losing both engines on one wing after wake turbulence resulted in high G-force roll, during the Gulf War. (And landed safely!)

Grissom Airmen share their Desert Storm stories

Jan. 16 marks the 25th Anniversary of Desert Storm and Airmen from Grissom were there to fuel the fight.Operating out of Jeddah, Saudi Arabia, members of the 434th Air Refueling Wing joined coalition

www.afrc.af.mil

 

[jb747]

Then there was this case of a US Air Force Grissom KC-135E tanker losing both engines on one wing after wake turbulence resulted in high G-force roll, during the Gulf War. (And landed safely!)

Good job it had the replacement engines. It wouldn’t have flown with only two of the originals. They were marginal with four.

Time for some discussion of g. It is simply a measure of acceleration. 1g is what you experience sitting in your kitchen. It’s always measured towards the floor of an aircraft. It can be positive or negative. If you go and hang upside down from your chandelier, you’ve got -1g. Whilst all flying is obviously within the Earth’s gravity field, it’s basically ignored within the aircraft. If I pull 6g from straight and level flight (i.e. the start of a loop), or 6g from inverted, it feels exactly the same in the coughpit. Everything would crash to the coughpit floor irrespective of the aircraft attitude. The difference, though, is that in starting from straight and level, my airspeed would be decreasing as the nose rose until reaching the top of the loop, whilst starting from top it’s rapidly increasing. The ability to achieve the g varies with the airspeed, so you can see that in the nose down case, it could rapidly get out of hand. That’s why loops are started from the bottom. Aircraft are built to handle much more positive g than negative. So, something like the A-4G was limited to 7.2 positive, and 2 negative. Airliners generally have limits of +2.5 to -1, and they’d start to shed pieces at about the +4 to -2 area. But, the issue with large aircraft and the g pulled during recoveries is what is called rolling g. If they are simultaneously being rolled and pulled, then the actual g loading will differ across the aircraft. The loading at one wing tip could double the g being measured in the coughpit. It all depends on how much roll input is applied, and the wing span. The upshot of this is that would be possible to shed items from one wing, even though the g measured at the coughpit is within the structural limits.

AF447 had a sink rate in the order of 20-30,000 fpm. It achieved this simply because it was no longer flying. The angle of attack was so extreme that it was simply an object falling through the sky. Something like the F-22 might be able to recover from 45º AoA, but no chance whatsoever in an airliner. The only reason that it didn't convert into a spin was that the yaw damper was very actively countering any yaw. But, it wasn't under any particularly high g loading, and stalled wings don't produce much lift. So, the fact that it didn't break up remains irrelevant to any discussion of rapid descents.

So, lets just go really fast. And we'll ignore any IAS or mach speed limits. What happens then? Well, because of way drag rises as the square of speed, you'll need increasingly low pitch attitudes to achieve and keep your high IAS (let's pick a number and call in Vmo +50). Max speeds are chosen for a number of reasons, and one of them is an effect called flutter. Basically the aerodynamic surfaces will start to vibrate, then literally flap, and then break off. If you happen to pull a bit of g, the flutter boundary will reduce, and breaking bits becomes even more likely. Higher up, where we're ignoring the mach limit, the centre of pressure will move aft, and the nose will tend to drop. Speed brakes may make this worse. Shockwave formation will start from around .9 mach and as it moves aft will reduce elevator effectiveness, meaning that you'll need more back stick to get the same g result. And if you happen to decelerate past the point to where the shockwave does this, whilst under g, you'll get a very rapid increase in g, without any change in control position. Test pilots play with some of the test things during flight testing, and that's how the limits are established. The average airline pilot is a very long way from being a test pilot.

 

[Quickstatus]

because of way drag rises as the square of speed,

Isn't the relationship between drag with respect to airspeed shaped like a U /parabola?

AF447 had a sink rate

Basically accelerating to earth at less than -9.8m/s2 due to air resistance ? And maybe at some point acceleration =0 (terminal velocity). At all times, G experienced would be 0<=G<=1?

convert into a spin

What causes spin in a stall?

 

[D747]

That's one fast reaction | By The 737 Handbook | Facebook

Can you explain what is going on in this video please?

 

[jb747]

Isn't the relationship between drag with respect to airspeed shaped like a U /parabola?

That's the total drag curve. It's made up of two components, that have more or less opposite behaviour. Form drag, which is basically the drag caused by the shape of the aircraft, skin friction, etc (i.e. what you feel if you stick your hand out of the car window) increases as the square of velocity. Induced drag comes from the creation of lift, and and rises with increasing angle of attack (in other words there's more if you go slow). Plotting the two together gives the U shape of the total drag curve.

aerodynamics of flight drag

Basically accelerating to earth at less than -9.8m/s2 due to air resistance ? And maybe at some point acceleration =0 (terminal velocity). At all times, G experienced would be 0<=G<=1?

I'd expect lots of buffeting, but yes, more or less 1g.

What causes spin in a stall?

Yaw. If the aircraft were symmetrically stalled, and you introduce yaw, then one wing will be moving forward slightly faster then the other. That will reduce its angle of attack, giving less drag, and more lift. That in turn will give roll, which will reduce it's AoA further (whilst increasing it on the other side). Which in turn gives more yaw....so, it's self supporting.

 

[jb747]

That's one fast reaction | By The 737 Handbook | Facebook

Can you explain what is going on in this video please?

Looks like an attempt to avoid a hard landing. Doesn't seem to have been any flare, and pulling the power is going to make it worse.

Mostly I consider this sort of stuff to be ineffective, with the potential to make it worse.

 

[straitman]

Isn't the relationship between drag with respect to airspeed shaped like a U /parabola?

This is a version of the graph you are referring to.

 

[jb747]

This is a version of the graph you are referring to.

It's amazing how much information is hidden in that simple graph.