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The dramatic loss of speed happens after the plane starts descending again.
And remember, the landing speed for Tu-154 is 250 km/h. They had to bring it down gradually from 300 km/h. But after the 1600m point it drops to below landing speed.
The dramatic loss of speed happens after the plane starts descending again.
And remember, the landing speed for Tu-154 is 250 km/h. They had to bring it down gradually from 300 km/h. But after the 1600m point it drops to below landing speed.
Well, then, to say the least, the approach was unstabilized by 1000ft (300m), which was well before the 1.6 km mark, and they should have gone arround at that early point (at least by most airlines' SOPs, even more with the all the head of a government on board).
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Since many accidents happened during approaches where parameters were not strabilized at the target values, the "stabilized approach" criteria was created several years ago and was adopted by most airlines.
The stabilized approach criteria has a treshold (usually 1000ft AGL in IMC and 500 ft AGL in VMC) at which, and from which, the approach should be stabilized. If it's not, or if it becomes stabilized after that treshold, an immediate go-around should be initiated.
The "stabilized" criteria includes several things like (examples):
Briefing completed.
Aircraft configured.
Airspeed Vref -0 +10kts
Glide slope +/- 2 dots
Vertical speed less than...
Airplane on track.
Minor corrections needed to keep these parameters stabilized.
If Vref was 250 Km/h, and they were doing better than 300 by 1000 ft or below, then by most airlines' SOPs the approach should have been called unstabilized and a go-around should have been initiated.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
Since many accidents happened during approaches where parameters were not strabilized at the target values, the "stabilized approach" criteria was created several years ago and was adopted by most airlines.
The stabilized approach criteria has a treshold (usually 1000ft AGL in IMC and 500 ft AGL in VMC) at which, and from which, the approach should be stabilized. If it's not, or if it becomes stabilized after that treshold, an immediate go-around should be initiated.
The "stabilized" criteria includes several things like (examples):
Briefing completed.
Aircraft configured.
Airspeed Vref -0 +10kts
Glide slope +/- 2 dots
Vertical speed less than...
Airplane on track.
Minor corrections needed to keep these parameters stabilized.
If Vref was 250 Km/h, and they were doing better than 300 by 1000 ft or below, then by most airlines' SOPs the approach should have been called unstabilized and a go-around should have been initiated.
A two-dot deflection on the glideslope at 1000 AGL in IMC is a go-around at most airlines I am aware of.
Well, then, to say the least, the approach was unstabilized by 1000ft (300m), which was well before the 1.6 km mark, and they should have gone arround at that early point (at least by most airlines' SOPs, even more with the all the head of a government on board).
That does not absolve anyone though from doing a thorough investigation and finding out what caused the crash.
That does not absolve anyone though from doing a thorough investigation and finding out what caused the crash.
Of course.
The only thing I intend to say is that I don't think that the scenario was:
"...the cause of the crash was a single significant event that happened about 1600m from RWY. The crew was going to take the plane to the NDB and push the "go around" button if no RWY in sight. Instead they had to scramble to recover from an unexpected steep descent. There is no indication of pilots error."
Specifically:
- I don't think that the crew did everything correct (lack of briefing, unstabilized approach, there could be more... I feel that "crew error" in some way will be a strong part of the chain of events. Now crew error is never the cause. Then it must be investigated how that error(s) happened and how it could be prevented.
- I don't think that there was a catastrophic airplane failure. The plane did arrest the descent and started to simultaneously accelerate and climb again after all. I do feel there was some kind of non-catastrophic failure that became critical due to the low altitude, like the thrust levers being retarded, a spoilers extension, a change of mode in the autopilot, etc... wich was eventually but too late correcred. What I don't have even a feeling on is whether that failure was a systems or human one (i.e. uncommanded or unintentionally/wrongfully commanded)
However, I do feel that this part is correct:
"The crew was going to take the plane to the NDB and push the "go around" button if no RWY in sight."
I must add that I feel that 100m above the runway (which in this case is a tad less above the ground where the plane finally crashed and quite less above the trees) is a too low minimum for a non-precision approach and even more for an NDB approach. It leaves too little margin to recover from anything.
(note the usage of "think" and "feel" along this post)
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
I will stick to my guns and with a cautious "I think" I will repeat that what happened around 1.6km was, I think, an irreversible event that brought the plane down. I can speculate that the crew made some mistakes before they got to that point, but that cannot be said for sure with the info we have so far. Everything about airspeed, rate of descent, being on glide slope or not is still a speculation. The CVR transcript is not reliable at this point. The best source so far, the video of the last 30 seconds, if comfirmed in official release, would point to some mistakes. But I will wait with the final condemnation till I know for sure. What I feel strongly about is that there was no pilots error in the last section of flight, when they reached 100m alt. The events surprised them and they did the best they could.
And I don't subscribe to the opinions that the flight should have never happened. By the same token you should never leave the house because something could happen just around a corner, or even better, you should never go on a road trip with your mother-in-law and your evil aunt as backseat drivers, especially if it rained at night, the roads are slippery and your tires are marginally good. If a wheel broke off during such a trip and you crashed into a tree, and the car company would try to blame you for everything surrounding the trip (maybe you even exceeded the speed limit slightly), you would not accept it lightly.
I feel the blame is going to go too much around the real cause of this crash because it is more convenient this way, or safer.
If the weather forecast was that marginal, it should have never happened at least without a backup plan. Some weather patterns for certain times of the year are more the norm and to treat it as just "another day" is absurd.
A friend likes to book his discount vacation cruises in the Caribbean in early September because that is when the kids are back in school and it's cheap. And, every year he is upset because they had to deviate and hide from the hurricanes. It's not cheap because the kids are in school and he knows that now; I honestly think he likes the drama.
Plan "B" could have been flying in when the weather was supposed to be clear and there was a wide dew point spread. Leave enough time to drive and that is a problem for the leader of a country where security is an issue.
I'm sure that I feel that.
I'm not sure that my feeling is right.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
... what happened around 1.6km was, I think, an irreversible event that brought the plane down.
What kind irreversible events could have done that?
Do you have a sort of mental list of possibilities? (like the short one I did)
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
... it should have never happened at least without a backup plan.
They had a backup plan. To divert to an alternate (be it before the aproach or after going around). They discussed it in the CVR.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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