Polish President and wife killed in Tu-154 crash

[Gabriel]

...throttle to lift time ...

Please define that. I don't even know what it is. In fact, I suspect that such a thing doesn't even exist.

[Evan]

Please define that. I don't even know what it is. In fact, I suspect that such a thing doesn't even exist.

It is the time between when you begin searching for throttle levers on a jet until the time they lift your drunken ass out of the cockpit.

[Deadstick]

Gabriel it's my understanding that there is a lag time between when you advance the throttles and the engines spool up on pure jets. I don't know this, but I remember reading an article in "Flying" magazine about how when flying a 727 you ask for power with the thottles and the three holes just stare at you for a few seconds. Maybe this isn't so much the case on more modern engines.

[MCM]

Deadstick - that is correct. There is still a significant lag. Thats not what Gabriel is talking about though.

Gabriel's point (quite correctly) is that thrust isn't what generates lift, and so by purely pulling back on the control column you can be generating additional lift before the thrust will come on.

However, due to the momentum on approach, the pitch up (and specifically time) required to actually create a positive RoC means that with no (or little) thrust the speed will have bled significantly. There is not a lot of excess speed when flying at Ref speed, and with so much drag with a high flap setting... you get the picture. So, yes, on approach, if you do not have thrust, you cannot practically arrest a rate of decent, because you run out of airspeed - but not because the thrust provides the climb.

In cruise, however, it might be a bit clearer to understand. If you are cruising at 290kts in level flight, and you quickly need to climb, all you do is increase the angle of attack (by pulling back on the stick). You do not need to touch the thrust levers to climb. The speed will change - after levelling off 1000ft higher you might be doing 250kts... but the climb is independant of the thrust levers.

Thats what Gabriel is getting at... "thrust to lift time" isn't a practical measure, because thrust doesn't create lift.

[guamainiac]

This is not meant to be a technical analysis of terms. How many of you jet types jockey down the glide slope on spoilers for just that reason? To have available power as soon as possible since the engines are producing some instead of being pulled back.

I think we all know that speed is what generates lift not thrust.

My point is that it is very probable that his lack of climb, because his throttles were pulled back and or, with his spoilers (combination) it could have never been a recoverable situation from that altitude.

[Northwester]

How do you get to that conclusion?

As I've said before, they hit the first tree below runway elevation, before the searchlight, and off-track.

Please refer to post #207 (I'd give the original source if I'd found it).

Be aware of the "confirmation bias".

I am not talking about searchlights placed 200m before the RWY. There was another searchlight near the NDB. Please look at the pics attached.

[kris]

This a/c had recently been upgraded with a radalt.

Apparently this aircraft was already equipped with radalt in 2008, perhaps also in 2006. This photo is dated June 06, 2006. Unfortunately I can't find any photo (nor details) of the recent upgrade.

[Evan]

I am not talking about searchlights placed 200m before the RWY. There was another searchlight near the NDB. Please look at the pics attached.

So you think they were looking for the searchlights, the 'gate', instead of the runway itself, and proceeded below MDA when they thought they had it sighted, on a glide path for 200m beyond the light? That's an interesting theory and would explain the steep descent. I can buy the idea that a pilot under that kind of pressure to land might descend at that point, confident that the runway would appear. But one thing still doesn't add up. I would expect some sort of communication on the CVR... something like "There's the searchlight". There's nothing to indicate any sort of decision being made. It's the lack of communication that doesn't fit here. It makes me wonder if something is missing from the CVR.

[Gabriel]

MCM, a short question.

You are on an ILS approach. You are the pilot flying.
At some point you get the "minimums" call (either from the PNF or the radalt) and the runway is not in sight.
Do you first set TOGA, then wait for the engines to spool up, and only then pull up to arrest the descent?

As a side comment (not specifically for MCM), the final approach speed in jets is at least 1.3 times the stall speed, and typically even more.
That's enough speed to instantly get 1.7 Gs.
The curved trajectory when you rotate for take off, when you flare, and when you go around, is calculated for 1.2 Gs.
You need less than 1.1 times the stall speed to get 1.2 Gs.

Now let's run an average example.
You are approaching with an indicated airspeed = true airspeed = ground speed (that is sea level, ISA conditions, no wind) of 140 kts, which is exacly 1.3 Vs (that means that Vs is 108 kts).

You are following a 3 degree glidelsope.

The vertical speed for 140 kts 3 deg NEEDS to be 740 fpm.

You hit minimums so you pull up at 1.2 Gs to go around.

Now the interesting thing is that 1.2 Gs is 386 feet per minute per second , which means that to arrest the descent of 740 fpm you need just 1.9 seconds. (in fact, that's 0.2 Gs but you need 1 G just to keep the plane flying at constant descent rate, so only the additional 0.2Gs count to arrest the descent)

Now say that during the maneuver you loss speed at the absurd rate of 5 knots per second (to get an idea, that's a typical acceleration during take off, you will never ever loose that much or close for pulling up 1.2 Gs).

In that case, you've lost 9.5 knots. You are not loosing any altitude anymore, and your airspeed is still 130.5 knots, which is still 1.21 times Vs, or enough to still enough to pull 1.46Gs if you wanted to.

Did I mention "throttles" or "thrust"?

Of course, the clock is ticking. If you don't get enough thrust soon you won't be able to keep the plane from descending for too many seconds.

But again, the operation is designed so you don't have to wait for the engines to spoo-up to initiate the pull up for a go around, but you can pull up and at the same time apply TOGA, and you'll arrest the descent (and start climbing) while you trade speed for vertical speed and wait for the engines to spoo-up. They will have enough thrust to sustain your speed and keep you calimbing before you've bleeded too much speed to make it dangerous.

There are a few ways to achieve this if it doesn't come "naturally".

One is to restrict the approach to a minimum "high drag" configuration so the engines are already pretty much spooled up to compensate for the drag.

Another is to use a Vref higher than 1.3 Vs.

Now, if when you start the pull up when you are doing 2500fpm (instead of 740) and flying at 1.15 times Vs (instead of 1.3 Vs), then there is no way to arrest the descent (you'll unavoidably stall in the process), unless and until you get significant ammounts of trhust, and if your thrust wasn't that significant in the beginning, that means waiting for the engine to spool up.

Ture for a B-747 and for a C-150. And yes, the 747 will have a much longer spool-up lead time than the C-150.

I'm sorry, but one can't beat Newton. Not even the pilots (many who tried are dead).

[Gabriel]

I am not talking about searchlights placed 200m before the RWY. There was another searchlight near the NDB. Please look at the pics attached.

Northwester, your analisys is flawed, and the descent profile you've traced is not right.

The place where the plane with the "8m" is depicted, is the precise place where the plane hi the first tree, 8m above the ground, below the runway elevation, short of the search light (and the OM antenna), and off center.

From there the plane keeps climbing almost along with the climbing terrain (damaging several trees that give evidence of that) until the left wing hits, and is sliced by, the bigger tree where the second plane is depicted.

So where you signaled "tire marks" the plane had already hit some trees before and was alrady climbing. Impossible that the pilot was aiming to touch down there.

Please don't fall in the trap. Don't use just the evidence that reinforces your model and trash the rest that doesn't. Beware of the confirmation bias.

[Northwester]

So you think they were looking for the searchlights, the 'gate', instead of the runway itself, and proceeded below MDA when they thought they had it sighted, on a glide path for 200m beyond the light? That's an interesting theory and would explain the steep descent. I can buy the idea that a pilot under that kind of pressure to land might descend at that point, confident that the runway would appear. But one thing still doesn't add up. I would expect some sort of communication on the CVR... something like "There's the searchlight". There's nothing to indicate any sort of decision being made. It's the lack of communication that doesn't fit here. It makes me wonder if something is missing from the CVR.

That's always possible. They were not able to decipher everything.

[Northwester]

Northwester, your analisys is flawed, and the descent profile you've traced is not right.

The place where the plane with the "8m" is depicted, is the precise place where the plane hi the first tree, 8m above the ground, below the runway elevation, short of the search light (and the OM antenna), and off center.

From there the plane keeps climbing almost along with the climbing terrain (damaging several trees that give evidence of that) until the left wing hits, and is sliced by, the bigger tree where the second plane is depicted.

So where you signaled "tire marks" the plane had already hit some trees before and was alrady climbing. Impossible that the pilot was aiming to touch down there.

Please don't fall in the trap. Don't use just the evidence that reinforces your model and trash the rest that doesn't. Beware of the confirmation bias.

The only difference I see here is the last part of the flight path, where based on CVR they were somewhat higher, and based on the other graphics they were supposed to be 8m above ground. One source is flawed. Don't know which one.

BTW, I am not insisting on this theory, just trying to explore it in depth so anomalies can be identified. I could easily adjust the flight path just slightly and maintain that it is still plausible. See below. But I see weaknesses in it too.

[MCM]

How many of you jet types jockey down the glide slope on spoilers for just that reason?

None? Certainly none I know would do that - but only because it isn't necessary. The aircraft are designed so - landing flaps are sufficient drag to ensure there is a "spooled up" approach thrust required for a normal approach.

MCM, a short question.

You are on an ILS approach. You are the pilot flying.
At some point you get the "minimums" call (either from the PNF or the radalt) and the runway is not in sight.
Do you first set TOGA, then wait for the engines to spool up, and only then pull up to arrest the descent?

Simultaneous - you pitch up and add power. You certainly don't wait for spool up to be complete. But that is assuming an approach thrust setting already. If for some reason you were going around with idle thrust set - you'd be being very very careful with your pitch until you had spool up.

[guamainiac]

Then why do I see the spoilers go in and out on approach?

The flaps are down but aren't they using the spoilers to maintain the glide slope?

And if not then why are there spoilers?

[MCM]

On some aircraft (read Boeing and Airbus at least) spoilers are used to aid in roll control, which may explain why you see them move on approach. When, for example, left roll is commanded, the left aileron AND some spoilers on the left wing will deploy, depending on the amount of roll commanded.

Spoilers are used to decelerate the aircraft in flight, aid in roll control, and to "dump lift" on the ground to ensure maximum weight on the wheels to allow efficient braking. It is very rare to use them on approach to slow down after you are stable on the glideslope - if you did it would be momentarily - and this is prohibited with landing flap in many aircraft anyway.