simongr

Wouldnt one factor not be the max length of a runway at one airport but the minimum length? You can not guarantee which runway you can use - so they may be able to fly off one, prep the aircraft for that and actually be flying off another which they can not fly from.

NM

I believe the Captain can request a specific runway to be used. Of course its up to ATC to decide if they will make that runway available. But if its needed for operational reasons then it unlikely to be refused. It may just take them a little longer to get to the requested runway.

But in the case of trans-Pacific ops, I think would find that even with 14,000 feet of runway available at each end, the payload restriction would still make the operation non-viable with the thrust restrictions imposed.

jb747

There are a couple of ways to look at that. Firstly, you obviously don't want to be pumping fuel into a tank that has a leak. But, that tank, until it is empty, has something you want...fuel. In many cases with a fuel leak, you'd attempt to feed all of the engines with fuel from that tank...to burn it before it leaked away.

Additionally, the ability to move/pump fuel is part and parcel of jettisoning it.

Lastly, even once the leaking tank is dry, you still need to manage the fuel you have left.

jb747

CofG has quite a wide range of acceptable positions. Normally the A380 takes off with the CofG at 39.5% (fuel is moved to the tail to achieve this), with the actual limit being 43%. In flight the aircraft operates at between 41 and 42% until the tail fuel is gone, and then the CG drifts forward. From the flight manual, it looks to be that any failure that precluded CofG control would give you at least 4 hours before reaching the limit..and the aircraft doesn't suddenly stop flying at that point. Assuming the worst case with regard to CG (i.e. #2 feed tank empty), the CG at landing would inside the aft limit.

No, not at all. Firstly the wings are made up of multiple tanks. Secondly the leaking tank(s) were close to the centreline, and thirdly there is a tank much further out, which contained appreciable fuel. In any event, the aircraft won't spin from an empty tank on one side. It would certainly be one wing heavy, but complete loss of the contents is well within the control capabilities, although it would affect approach speeds, and helps explain why pilots do controlability checks.

jb747

Not at all. The ATSB will, at some point, declare that they are finished with the aircraft, and repairs will start. That will be in a much shorter time frame, and could even have happened already.

jb747

Like all good stories, not quite true. They were using reverse on all landings, but only idle reverse. Contrary to popular opinion, reverse thrust does precious little actual reversing. A 60,000 lb engine may produce a couple of thousand pounds of reverse...at full reverse thrust. Almost all of the effort involved in stopping an aircraft comes from the brakes. There is more braking effort provided by the wheel bearings (about 12,000 lbs) than there is from four engines in full reverse. Of course, reverse, even idle, also has the effect of cancelling the forward idle thrust.

What was not understood was the contribution made by reverse to blasting water off a wet runway, and so giving the brakes some level of grip. Airbus haven't learnt this lesson yet, as shown by their reluctance to fit reverse to the 380, until forced to do so by the FAA.

The problem in BKK though was that the #4 thrust lever wasn't quite closed. That inhibited reverse thrust on all engines, and because the aircraft had flicked back to air mode, it also stopped the spoilers from rising. If anything the spoilers had a far bigger effect on the outcome than anything else.

jb747

The problem is twofold. Firstly, heading east from Australia you generally have tailwinds, so the fuel requirements are less, and the aircraft are lighter.

Secondly, 07L/25R at LA is not available for A380 ops, as it is too close to the parallel taxiway.

jb747

The thrust settings on the A380 are just that. Not RPM, not EPR, but % thrust. This is the case in the normal FADEC mode. If it falls back to Alternate or Degraded, the limits and displays are % RPM based.

jb747

No. At most airports the shorter runways are either not available to the 380 at all, or are so performance limited to be useless.

Yes, it is quite possible that in some weather conditions, you will not be able to take off, perhaps more to the point, won't be able to take off with a viable load. That applies to all aircraft. That's often seen in Oz, when the crosswinds at Sydney preclude the use of 16/34 and aircraft on long ops fly up to Brisbane to refuel, or perhaps drop in at Darwin, Perth or Melbourne.

number_6

Except that the A380 switched to alternate law (for reasons that are still not understood, at least per my sources) -- which means most of the flight laws that prevent this (complete loss of control) were inoperative. It was up to the skill of the pilots to keep the plane flying (the software basically said "too hard, give up"). They tried to pump fuel from the outboard wing tank to the center tank, but part of the engine shrapnel damage cut the wiring needed for that process (primary and not-so-redundant backup). Actually this is one of the most severe outcomes of the uncontained engine failure, that so much damage to so many crucial systems could occur ... far more than the design called for. A tribute to both the aircraft engineering and to the crew that they landed safely.

I didn't remember that part of it (spoiler failing to deploy). That of course also affects the efficiency of the brakes and anti-skid system, so probably that is greater effect on stopping power than the reverse thrust. I do know that reverse thrust is typically only 40% reverse (as there is still forward thrust present), and rarely more than 20% of the stopping power. All airplanes are certified without reverse thrust. The primary value of using reverse thrust on dry runways is to keep the brakes cooler and reduce the turnaround time. But BKK was very wet (torrentially so), and reverse thrust was needed to overcome the aquaplaning. Still a very sad event for QF.

The one aspect of QF32 that has not gotten a lot of public recognition is the great skill of the pilots in handling the failure, including dealing with multiple unexpected failures that I suspect were "not in the book" and not the way the simulator did them!!!! They deserve a lot of praise for being so competent and having an understanding of the way the airplane works and of the situation when deluged with system failures and unhelpful software.

jb747

Not really. All depends on the weather. Off a 4000 m runway (nil wind, 36°, max weight), you can go at FLEX 40 with flaps at 1+F and air conditioning off, or at Flex 37 with Config 2 and air on. But, at 37° Flex 37 actually equals TOGA, so I guess this is going to be very limiting through summer.

jb747

You'd better get your sources back to their books. The reversion to alternate law I was an easy to predict consequence. I've flown an A380 in alternate law (though I was in alt II). The aircraft is no worse mannered than a 747 (which, let's face it, spends its entire life in direct law). The software didn't 'give up', but it reverted to alternate law as the mode best suited to the aerodynamic configuration.

There is no centre tank. All they wanted to do was jettison some fuel. There actually wasn't much they could get rid of, as you cannot jettison feed tank fuel (and they would have contained around 80 tonnes). The loss of AC bus 1 and 2 most likely explains this.

Well, in Oz the media just loves throwing mud at QF, so admitting that it trains its pilots properly is something that sticks in the craw. There is no doubt that they did an absolutely superb job, and maintaining the discipline to logically work through their problems was a major part of that.

number_6

Several Airbus crashes were directly due to unexpected airplane behaviour when switching flight laws unexpectedly -- but these were some years ago and Airbus spent a lot of effort in putting the fly into fly by wire. Good to hear that the A380 has such good behaviour. Even the chief test pilot at Airbus died in a CFIT crash when testing exactly what you described (in that case reversion to alternate law during landing; his attempted go around, a planned exercise, sadly wound up being below runway height). A lot of blood has been shed in perfecting that flight control software.

One curious facet of the QF32 was the repeated autopilot disconnect during landing; is that also normal or predictable? The PIC tried to reengage it several times per ATSB report before giving up and landing manually (in what I call a very difficult landing that was perfectly executed).

og

Thankyou jb747 for your postings. Most appreciated.

jb747

From what I've heard, the drops out were expected and understood by the crew at the time. It didn't like how slowly he wanted it to fly, but would reengage with a couple of knots speed increase.