Stopping an airplane

I’ve been watching the news on the Air France flight that went off the end of the runway in Toronto with much interest (particularly since it happened while I was away from home on a trip).

One thing has been puzzling me - much has been made of the fact that the water (from storms) on the runway made it much harder to stop, and given that the plane landed far down the runway it made it impossible to stop in time.

I thought planes used their reverse thrust to slow down to something near taxiing speed (in which case I don’t see the relevance of the wet runway other than maybe making it harder to steer)? Do the big jets also use wheel brakes to slow down after landing?

As an aside, I landed last night in the middle of a thunderstorm - lots of lightning, but surprisingly there wasn’t a lot of turbulence. After only a few days after the incident in Toronto, landing in bad weather takes on a new “significance” :eek: .

They use thrust reversers, anti-lock brakes, and spoilers that extend from the surface of the wings to slow down after landing.

Assuming these system worked correctly, the probable cause of the accident was the late touchdown. The water on the runway may have been a contributing factor.

Airplanes (large jets) use both reverse thrust and wheel brakes for stopping!

Apparently 747s can use just wheel brakes. I’m guessing it depends on the length
of the runway. Like, why tax and shorten the life of the engines if the runway
is long enough!

The automatic braking system on Boeing B747-400 series aircraft allows the crew to pre-select a desired deceleration rate during the landing roll (there are six settings: RTO, for rejected take off, 1, 2, 3, 4 and MAX). Brake torque is automatically adjusted to achieve a programmed rate of deceleration depending on, among other factors, the amount of reverse thrust that the crew selects. For example, at a given automatic brake setting, if reverse thrust is not used, higher brake torques would be required than if reverse thrust is used. The PF had selected auto-brake setting three and idle reverse thrust in accordance with the curfew requirement.

Oh, OK. Thanks!

From what I’ve seen they touched down 4000’ down the runway with a tailwind.


Long landing + tailwind = end of the runway coming up really fast.

As for the autobrakes: I don’t know how Airbus wires them but Boeing has the various settings tied to a deceleration rate. For example if you select “Medium” on the autobrakes you will get a 7 ft/sec/sec deceleration. If you use thrust reversers it just means that the brakes work a little less to achieve that same deceleration.

That being said you can always stomp on the brakes yourself and override the autobrake system, which is an instinctive reaction when you see the end of the runway approaching at high speed.

I believe planes have some of the most sophisticated braking systems in existence - they are supposed to be able to haul them down from flying speed to standstill double-quick even if everything else (including engines) go pop.
I remember seeing a documentary on the 777, featuring a segment where it had to meet an FAA braking requirement, which was something like being able to stop from takeoff speed, fully loaded, within a set (short) distance and then taxi around for 5 mins afterwards. After coming to a halt carbon-fiber disc brakes were glowing white hot, and eventually set fire to the tyres purely through conducted heat. The entire set of wheels basically melted and were destroyed. It was very impressive.
A quick google found this link with a mention of the brakes for the new Airbus A340

So… Around the water cooler in the pilots’ lounge is that pilot being described as an idiot for attempting to land that far into the runway in adverse weather, or hailed as a hero for bringing the airplane down in bad conditions without killing anyone?

I’d have to say the answer is probably “Yes”. Would depend greatly on the holder of the opinion of course. Pilot should have landed farther back (hell, he shoulda landed in a headwind if he had a choice, which he might not have had at the time), but everyone makes mistakes and hindsight is 20/20. That said, it sounds like it was a hell of a difficult landing under the circumstances.

Indeed. But when your mistake results in a bunch of injuries and the destruction of a $100 million aircraft, don’t be too surprised if you are not soon granted the chance to repeat it.

I haven’t read details on this, but if the pilots put the plane down long on the runway with a tailwind before ever trying/considering their alternate airport, then I’d say it’s piss poor judgment. The only time I’d put a plane down in those conditions is if there was something wrong with it which makes further flight unsafe. I originally heard passengers saying that power went out in the cabin before touchdown, but I haven’t heard anything else about that, so I don’t know what was going on.

This may be a bit like the Air Transat dead stick into the Azores a few years back–the pilots (from what I understand) did some questionable procedures which most likely drained their fuel unnecessarily, but since they got everyone on deck in one piece, they were seen as heroes.

The tower would have assigned the runway (and would know the wind direction), the crew wouldn’t have chosen it. But remember this was in a severe thunderstorm, with microbursts all over the place. What had been a headwind could have turned into a tailwind so suddenly that no action could have saved the plane, and the tailwind itself could have accounted for the long touchdown. That said, the posited microburst must have been right in line with the glidepath, since the plane tracked the runway perfectly anyway.

Look for the ultimate assignment of blame to be on the pilots, yes, that’s traditional, but for electing to land into a thunderstorm. Contributing factor might be ATC for not providing sufficient warning, and perhaps to Transport Canada (or whoever the responsible agency is) for not installing enough microburst detectors at YYZ.

It’s really neither of these. They certainly weren’t idiots - you don’t get to the left seat of an A340 by being an idiot.

What most of us are asking is “What were they thinking?” Put more precisely, what chain of events led those guys to attempt the landing, and not go-around after they touched down so far down the runway?

They did not intend to go off the end of the runway. So the question focuses on their decision-making process: it led them to a bad decision.

At this point any ideas are pure speculation, but there are some things that will be looked at. Their training with Air France, for example. Had they recently flown into similar weather with normal results? The aircraft in front of them landed safely, so maybe there was a violent wind change close to the ground. Does the “culture” at Air France discourage go-arounds? After all, a go-around in an A340 can cost upwards of $3,000 in fuel alone. Does the company unkowingly pressure pilots into thinking they have to get it down the first time?

I don’t know the answers to any of these questions, but eventually they will be answered. What pilots can then do is look at how these guys got into the situation they did, and take steps to prevent it from happening again. That might mean more windshear detectors at Toronto, a change in the training program at Air France, a change in policy at Air France, or any combination of these and other (yet unknown) items.

Unfortunately it will be a while before we have any definitive answers.

Back in (I think) '99, a Qantas 747 ran out of runway when landing in Bangkok, and it ended up in a golf course. The cause of this accident was that Qantas management had allegedly ordered air crew to use brakes only and not reverse thrust, in order to save fuel. What I have never understood is why, when the pilot (who had been warned the runway was slippery) realised he was going too fast, he didn’t think, “Bugger management, I’ll deal with them later. Right now I’ve got to stop this plane, and I’ll use reverse thrust”. But for some reason, that didn’t happen.

In later managerial shenanigans, the damaged 747 was repaired at greater cost than the purchase of a new one, so they could keep saying “Qantas has never lost a plane” (and for insurance purposes, I believe).

Most airplaines that land on wet runways make safe landings. Why would the water on the runway make any difference in this case?

and somebody else mentioned about not having enough windshear detectors. I may have misheard, but I think it was mentioned on the news that Canadian airports don’t have any windshear detectors.

From what I’ve seen they touched down 4000’ down the runway with a tailwind.


Long landing + tailwind = end of the runway coming up really fast.


On the news today…further data is that the runway is 9000 feet long, and under ideal conditions, at their touch-down speed, it would have taken 5000 feet to stop. So, not much margin left.

A wet runway increases your stopping distance in an aeroplane the same way it does in a car. If there was standing water on the runway the aircraft might aquaplane in which case the wheel brakes will do nothing until the aquaplaning stops.

So the water probably made the difference between just pulling up in time (if it was dry), and running off the end at speed.

Heck, you may be right. I don’t know off the top of my head if Toronto has a LLWAS system (Low Level Windshear Advisory System) in place or not. If I had to guess I would say no, since violent thunderstorms are rarer in Toronto than they are in, say, Dallas. But my Jeppesen charts are in Memphis so I can’t check. :cool:

Another airport item that has been brought up is the lack of any significant overrun on the runway. Airports with little or no overrun (think La Guardia - short runways that end in the water) present more danger than ones with plenty of overrun. In Toronto the problem is that the runway ends in a ditch - at least one other aircraft (a DC-9) has ended up in that same ditch. If the airport filled in the ditch and paved the new ground (or installed some of the new crushable concrete at the end) this could have been a much less severe accident.

As to the wet runway - yes, it makes a significant difference in stopping distance. Some airports have grooved runways to prevent standing water, while most have the runway “crowned” - the center is higher than the edges so water will run off the sides. What could have happened to the Air France crew is the worst possible scenario - they touch down long (4000’ down), and have normal braking on a wet runway (with, as previously mentioned, a 5000’ stopping distance). This should have them stopped at the very end of the runway, but still safe.

Unfortunately the runway surface is not uniform - the last 2000’ that they are trying to use to stop is also the touchdown zone for that same runway when the wind is out of the east. This means that there are rubber deposits from aircraft touching down over the past months - right where this crew needs all of the airplane’s stopping ability. If anyone has tried to drive/stop on wet rubber deposits, you know that your deceleration decreases dramatically.

This is normally not a problem for airliners - look at any runway and notice where the rubber deposits are. They are within 2000’ of the ends of the runway. Approaching from either end you normally touch down in the rubber deposits and then begin braking on clean runway. Only in extreme situations would you be trying to max brake the airplane on the opposite end of the runway, covered in deposits from aircraft landing in the other direction. But this is what happened to this crew - and for an added bonus the rubber was wet.

I’ll bet dollars to donuts that their braking efficiency decreased significantly over the last 2000’ feet, which contributed to them going off the end of the runway. That wasn’t the cause of the accident (landing long and with a tailwind might be), but I’ll bet it gets cited as a contributing factor.

“It is the Superior Pilot who uses Superior Judgement to avoid situations requiring Superior Skill.”

Sadly, the best way to having superior judgement is learning from others’ mistakes. When I was doing my ground school training, there was some singer who died when her plane was overloaded and crashed. So that day our instructor emphasized the importance of loads and balances. He emphasized that while it may have been the singer’s decision to bring the extra baggage, it was the pilot’s decision to make sure his plane could handle the extra load, or to abort the flight all together until the load was lightened. :frowning:

The runway length is 9000 feet. I had thought that YYZ essentially turned what would have been an overrun into simply more runway.