Available Data and VNE
Walter,
I was trying to stay out, but your last entry does need challenging. Look up the word "available" in the dictionary.
I have stated earlier I know/ knew quite a lot about low level navigation, meteorology and flight safety. I know little or nothing about computer flight simulations.
Even so I read the Boeing report and could not understand how they could replicate the final flight of ZD 756 without ADR inputs. I asked lots of "experts". They told me it was impossible to do so.
Earlier in this thread Boeing admit that the simulation shows what "may" have happened, not what "did".
HOL para 132.
" we conclude that it would be quite inappropriate to treat the results of the simulation as proven facts."
If you are using the simulation to show that Holbrook may have been wrong, fine. If you are tring to disprove his evidence it just does not wash.
Instead of trying to rubbish the evidence of the last credible witness, why don't we use the few available facts to see if he could be right.
Much has been made about the high speed transit and possible breach of VNE. We do have a Take Off time (ish). We do have a time of impact, (precise or ish) depending on the TANS. We know the distance between the two points.
Everything I have read, points to an average Groundspeed at or just above 150kts.
Let us simulate the flight:
The crew get airborne already knowing they are up against crew duty restraints. They are going to fly as fast as conditions allow.
VNE is 160 but that would involve uncomfortable vibration for the pax.
I am told by an experienced Chinook operator that an IAS of 150 is realistic and in most conditions comfortable. They are likely to choose that speed.
We have from forecast ( and some actuals) an estimated tailwind of some 15 - 20 kts.
If the crew maintain 150IAS or 165 - 170GS. They are going to arrive early at the crash site. To make T/O and impact times fit, part of the sortie has to be flown at a lower speed.
In all probability they maintain 150 until approaching the coast. In marginal conditions they would then "thr (sorry Robin), slow down" until they were certain of their position and could see the coast. Just good common sense and airmanship.
Any evidence to support this hypothesis? Well yes, MR Holbrook our eyewitness. He would have seen them at this stage of flight.
We know from the evidence of Mr Cable that impact was aroond 150IAS 174 GS.
Very few people dispute Mr Holbrooks version of the weather. The visibility was 1 - 2 nms. The crew almost certainly could see what Holbrook could see.
Arthur Rowe explains why he thinks Holbrook was wrong. But even if the Chinook was at double his (Holbrooks) minimum estimated GS,(of 60 to 80 kts GS), there still needed to be a significant increase in GS between sighting and impact. Far more than could be explained by an increase in tailwind over the cliffs.
Having slowed down from 150IAS to something between 60 and 120, why did they decide to fly faster into deteriorating weather. In all my 10,000 hours I have never encountered a pilot who choses to accelerate into worsening conditions.
To me the answer is fairly obvious:
a. They had no control over the aircraft.
b. They thought they had a lot more time to react than they did.
If I bite again on this subject, please feel free to shoot me.
Last edited by dalek; 10th Jun 2010 at 21:40.