Deadly plane crash at Aspen airport

[PilotDAR]

The view presented by Camera 4 shows pretty strong wind blowing snow around on the apron, which certainly looks mostly like a tailwind for landing. I don't know much about landing Challengers, but that looks like 15 to 20 knots to me, and that's gotta affect how the plane lands.

Seeing the video, it appears to me that the pilot hit the nosewheel really hard, which is easy to believe in a downwind landing. The heat which is apparent at the nosewheel suggests maybe a burst nose wheel tire, and overheated rim? Then the pilot appears to me to way overcorrect for slamming the nose down, and gets airborne again. If the pilot did not add power for that, the plane was simply landing much too fast, if it would become airborne again so easily during a bounce. Landing much too fast in airspeed is a pilot mistake for overcompensating for the tailwind the pilot must have known that they had.

So, yes, PDW, this DOES appear to be variable tailwinds on final....

[arctic_slim]

Holy crap, the plane pitches down pretty violently after that bounce/go around attempt. At first I thought maybe it bounced back up and stalled but the pitch down is pretty violent. I wonder if one of the pilots pitched forward.

[PilotDAR]

As I have said, I'm not a Challenger pilot, but if, through a poor touchdown, the nose slammed down (and maybe broke something) a startled pilot might over rotate to correct, and then recognize that, and pitch down too much to correct. A really poorly executed flying boat landing can look like this....

[Sidebar]

From the camera 5 video, it looks like about 20-25 degrees nose down pitch just before the crash.

[Troubleshot]

Maybe the violent destruction of the nose gear broke a control cable up front somewhere? or maybe pilot seat slid forward or something?

crazy footage....

[Trematode]

Yeah that camera 5 footage is alarming.

Looks like he bounced a couple times before the last one, and then the aircraft violently pitches down, even while inertia is still carrying them upward. Scary, and I'm not ashamed to say I've got no clue what's going on there.

[pdw]

To get an idea how there's still "upward inertia" while the nose "violently pitches down" there, it might help to explore airspeed fluctuations from the point where it still looks good in the flare. How does the high-mounted engine thrust affect pitchdown at the high point of that second (full power) bounce ?

Seeing the video, it appears to me that the pilot hit the nosewheel really hard, which is easy to believe in a downwind landing. The heat which is apparent at the nosewheel suggests maybe a burst nose wheel tire, and overheated rim? Then the pilot appears to me to way overcorrect for slamming the nose down, and gets airborne again. If the pilot did not add power for that, the plane was simply landing much too fast, if it would become airborne again so easily during a bounce. Landing much too fast in airspeed is a pilot mistake for overcompensating for the tailwind the pilot must have known that they had.

So, yes, PDW, this DOES appear to be variable tailwinds on final....

The videos show the approaching aircraft did well on final ... and does not seem to be an issue. So we're talking only about the touchdown components here causing a problem at touchdown. The aircraft appears very fast during the flare; yet seeing this ATIS info and Video evidence about the high runway winds on the tail means the 10kt+ fluctuating airspeed must have already been down very low at the point where the wheels are touching for the first time (spinning them up also slows more) at a super high ground speed, ... so in adding power there a slow-airspeed porpoise of a lightly loaded aircraft has already set up.

Early in their touchdown zone and flare there's a hint of a rise prior to the first runway contact, ... possibly the airspeed increasing as the Challenger catches up to a slower wind / gust while under the very high ground-speed condition where overtaking those component-changes induces instant airspeed-change toward either slow or faster airspeed.

The engines take a few seconds to reclaim 10kts there ... yet the same 10kts can be lost in catching up with the fastest tail-gust there (video # 3 & 4 ... shows the rapid /most-parallel tail component on the runway).

The second contact with the runway has the engine flashes visible, the engines are spooling for "Go-around Go-around !" ? .. and the third runway contact is the impact explosion where the added power is obviously not yet enough to have increased airspeed sufficiently to the point of stability despite a very visible high speed down the runway (somewhere near 50kts higher than the opposite landing direction would have yielded in that case).

[Colonel Sanders]

Look familiar?

http://www.youtube.com/watch?v=NMmHYWjEmkY



http://en.wikipedia.org/wiki/Pilot-induced_oscillation

Pilot-induced oscillations are sustained or uncontrollable oscillations resulting from efforts of the pilot to control the aircraft and occurs when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to cover the aircraft's reaction to the previous input with an overcorrection in the opposite direction.

An aircraft in such a condition can appear to be "porpoising" switching between upward and downward directions.

The most dangerous pilot-induced oscillations can occur during landing. Too much up elevator during the flare can result in the plane getting dangerously slow and threatening to stall. A natural reaction to this is to push the nose down harder than one pulled it up, but then the pilot ends up staring at the ground. An even larger amount of up elevator starts the cycle over again.

http://www.youtube.com/watch?v=XHPv0qt03aA

[bizjets101]

[burhead1]

airspeed increasing as the Challenger catches up to a slower wind / gust while under the very high ground-speed condition

???

Too fast, overcorrection and tail wind beyond the limits of the aircraft.

[cgartly]

Not sure if this is the right place for this post but anyways here goes.

I'm just a PPL with a basic understanding of how relative air movement effects a planes ability to fly so please forgive my ignorance.

In my basic understanding as long as you keep an appropriate indicated airspeed, why does it matter if you land with a tail wind?

I understand that the higher ground speed will result in using much more runway.

I fly out of a sometimes busy airport (CYLW) with only one runway and mountainous terrain (not nearly as steep as around Aspen and only 1421' above sea level) and on a lot of occasions land with 5-7 kts of tailwind. The control tower here likes to keep the runway with the ILS active as much as possible.

On one occasion I was on a 5 mile final with jet traffic ahead of me and a 737 a few miles behind me and the wind at the airport changed to 10g21 (direct tailwind) and I was offered a runway change, knowing that if I took a runway change I would force the 737 to also take a runway change I opted to accept the tailwind and simply added 6 kts to my final approach speed to account for the gust factor and landed without incident. The 737 turned down the runway change as well and landed normally. The only difference was I used some more runway and some of the illusions were different with the higher ground speed. I was flying a Piper Tomahawk by the way.

Was that stupid on my part? After reading this thread and watching the video's I am second guessing myself but still feel as long indicated airspeed is maintained and you have sufficient runway a tailwind shouldn't be a big deal.

[Colonel Sanders]

The higher the groundspeed, the easier it is to PIO.

Simply put, the faster things are happening, the harder
it is for you to keep up with the control loop, and the more
likely it is that you will push when you are going down,
and you will pull when you are going up, resulting in the
divergent oscillation known as a PIO.

Sure, you can land with a tailwind. I did an airshow in
Honduras with Freddy in a couple of Pitts S-2C's, where
we did head-on takeoffs (with 1/2 cu-8's at the end of
the runway) to start our formation routine, and we did
a head-on landing at the end. 20 knots of wind down
the 10,000 foot runway. Guess who got the tailwind
for the takeoff and landing?

Back on topic ... it's pretty obvious why the Challenger
is only permitted 10 knots of tailwind.

[Stallspin]

That's a pretty violent nose down. Stick pusher?

[Pratt X 3]

With aft mounted engines, like on the Challenger, the thrust line is above and behind the c of g. So when thrust is increased, there is a tendency for the nose to be pushed down. This is usually demonstrated the first time a pilot does a 2 engine go-around and unless they are prepared for it, the opposite effect than desired happens. Luckily, the first time it happens, the pilot is in the simulator and nothing more than their pride is hurt as the sim instructor explains the situation as they reset. This could be an explanation to the nose down movement shown on the video.
As for the stick pusher activating, most transport category aircraft with a stick pusher will have a radar altitude that the pusher is deactivated. Somewhere in the range of 800' to 1500' radar altitude. Below that, the stick shaker is still active but you won't get the pusher.

[burhead1]

I was offered a runway change, knowing that if I took a runway change I would force the 737 to also take a runway change


still feel as long indicated airspeed is maintained and you have sufficient runway a tailwind shouldn't be a big deal.

Who cares what you may make the other aircraft have to do. The controller may tell you to leave and re join or may have the other aircraft do the same. DON'T jeopardize your life because you don't want to upset the other guy.

What does you POH Say for tail wind?
Harder on gear, tires, brakes, longer runway needed, higher ground speed(you screw up and you could be dead as apposed to might be dead)

[Jet Jockey]

On one occasion I was on a 5 mile final with jet traffic ahead of me and a 737 a few miles behind me and the wind at the airport changed to 10g21 (direct tailwind) and I was offered a runway change, knowing that if I took a runway change I would force the 737 to also take a runway change I opted to accept the tailwind and simply added 6 kts to my final approach speed to account for the gust factor and landed without incident. The 737 turned down the runway change as well and landed normally. The only difference was I used some more runway and some of the illusions were different with the higher ground speed. I was flying a Piper Tomahawk by the way.

Was that stupid on my part? After reading this thread and watching the video's I am second guessing myself but still feel as long indicated airspeed is maintained and you have sufficient runway a tailwind shouldn't be a big deal.

First, I would not think for another aircraft. Do what is required from you for your aircraft and don’t mind the other aircraft’s situation. Chances are the tower would have sequenced you behind the landing 737 anyway.

Second, it is not stupid to land with a greater tailwind of 10 knots if your aircraft is certified to do so. Follow the AFM’s limitation and you stay out of trouble. Going beyond that opens a can of worms if an accident were to occur (getting sued and insurance company not paying).

Now this said it doesn’t mean an aircraft cannot fly properly (physically and technically) with a tailwind greater than 10 knots but it might be a bit more difficult under certain circumstances. Keep in mind that anytime you do so (under “normal operation”), you become sort of, of a “test pilot”. The aircraft manufacturer will claim they never tested beyond the limitation and that you were flying outside the aircraft’s envelop. In other words you are on your own to defend your actions.

Most aircrafts have a 10 knot tailwind limit (sort of an industry standard). Aircraft manufacturers limit the cost of certification by sticking to a “standard” and it seems 10 knots for a tailwind is it.

Indeed all the jets I have flown (Fokker 28-1000/2000 and 4000 series, Hawker 125-700/800 series, Challenger series and Global Express have a 10 knot tailwind limitation as defined in their respective AFMs.

In the airliner turboprop aircrafts that I have flown in the past, the Dash 8 is also 10 knots. However you can buy from Bombardier (I’m sure at a great cost) a supplement that allows you 20 knots. This means extra flight testing and certification is/was required.

The only one that I flew that allowed greater tailwind for takeoff and landing in its AFM (without a supplement) was the Dash 7. It allowed 15 knots tailwind for takeoff and 20 knots tailwind for landing with a flap 25 configuration. Flap 15 and 45 were limited to 10 knots.

The following aircrafts have all a 10 knot tailwind limitation to name a few…

Gulfstream G IV, Cessna Citation, Falcon 900, Boeing 767, Airbus 319/320/321.

The Boeing 737 and 757 have a “normal” tailwind limitation of 10 knots but like the Dash 8 above, you can buy from Boeing a supplement that increases this limit to 15 knots.

[Trematode]

Something else to think about with regards to tailwinds is that they are rarely from directly behind, especially if you are on an approach for one runway, the winds shift, and the airport is in the midst of switching operational runways. In my experience, if I have accepted a tailwind it is mostly a crosswind with a smaller tailwind component than the wind speed alone might imply.

A direct tailwind of 10g21 as the above poster mentioned is not something I would be comfortable with. However, If the winds happen to be 110 degrees off, the crosswind would definitely be more of a concern than any tailwind for me, personally.

In the end if there's a cross runway that it favors instead, that's the no-brainer decision.

[Jet Jockey]

With aft mounted engines, like on the Challenger, the thrust line is above and behind the c of g. So when thrust is increased, there is a tendency for the nose to be pushed down. This is usually demonstrated the first time a pilot does a 2 engine go-around and unless they are prepared for it, the opposite effect than desired happens. Luckily, the first time it happens, the pilot is in the simulator and nothing more than their pride is hurt as the sim instructor explains the situation as they reset. This could be an explanation to the nose down movement shown on the video.
As for the stick pusher activating, most transport category aircraft with a stick pusher will have a radar altitude that the pusher is deactivated. Somewhere in the range of 800' to 1500' radar altitude. Below that, the stick shaker is still active but you won't get the pusher.

It's not the "AFT" position location of the engines that creates the pitch down moment when full thrust is applied but their "high" mounted position. A B737 with its "Forward" but low slung engines below the wings has a pitch up moment when full thrust is applied on a G/A.

On the Challenger this is very noticeable when practicing stalls when the thrust from the high bypass fans kick in the pitch down moment is delicate to manage. If done to fast or abruptly you will get multiple stick pusher activations like riding a seesaw.

And no there is no limit at which altitude the system activates. Whether 28,000 feet or 50 feet the pusher will activate if the parameters require it to do so. There are two ways to disable the system which is done for an "abnormal" situation. There are two switches on either side of the cockpit at each pilot's position. Either one or both can be switches to the "OFF" position and this will deactivate the pusher system. The other way is to push and hold the A/P disconnect switch on either yoke.

As for "most transport category aircraft with a stick pusher will have a radar altitude that the pusher is deactivated", I don't know. The FK 28 did not have such system, neither does the Hawker, Challenger, RJs and Global Express. Most Boeing aircraft (if not all) don't have a stick pusher and I believe the same is true of the Airbus aircraft.

[pdw]

The higher the groundspeed, the easier it is to PIO.

Simply put, the faster things are happening, the harder
it is for you to keep up with the control loop, and the more
likely it is that you will push when you are going down,
and you will pull when you are going up, resulting in the
divergent oscillation known as a PIO.

Flaring in that very high ground speed over pavement that is never perfectly flat would expose any waviness in the pavement, even the slightest amount.

[Rookie50]

Something else to think about with regards to tailwinds is that they are rarely from directly behind, especially if you are on an approach for one runway, the winds shift, and the airport is in the midst of switching operational runways. In my experience, if I have accepted a tailwind it is mostly a crosswind with a smaller tailwind component than the wind speed alone might imply.

A direct tailwind of 10g21 as the above poster mentioned is not something I would be comfortable with. However, If the winds happen to be 110 degrees off, the crosswind would definitely be more of a concern than any tailwind for me, personally.

In the end if there's a cross runway that it favors instead, that's the no-brainer decision.

Way way too strong a tailwind for me in a heavier single. I'll land with 5 knots tailwind, that's it. Risk of runway loss of control just goes way up.