If a helicopter landed on my roof? I would either expect the roof to collapse straight away or to stay up. In the case of the Glasgow pub, the roof stayed up for several seconds after the impact, and then it collapsed. (It stayed up long enough for the band to make a joke about it.)
Can anybody explain the mechanism whereby that would happen like that?
GB expressed precisely :
Obviously, it was just margininally too weak to support the load and developing weaaknesses suddenly let go. Try bending a thick twig, it will begin to crack and then sudenly let go completely if the same strain is maintained.
The lift from the rotors reduces as they slow to a stop.
Personally, I think it's great that the Gov't has such a golden opportunity to save a fortune. They can disband the AAIB and spend a fraction of the money on propping Usenet up. Win-Win.
I believe it crashed, rather then landed, but that doesn't invalidate the question.
The force on the roof was probably not enough to cause immediate fracture of all the structural components but enough to overstress them, or perhaps fracture some over stressing the remainder, such that there was a progressive failure resulting in ultimate collapse.
Given that it was a twin engine helicopter, with an experienced pilot, I suspect they stopped some time before it hit the pub.
Colin Bignell
Google autorotate
it shouldn't have come down *that* way.
investigation will discover why.
On 01/12/2013 19:43, Apprentice 65 wrote: ...
AVTUR has a minimum flash point of 37.8C, although the median of a large number of samples tested by the FAA following the loss of TWA flight 800 in July 1996, was 53C. It also has a relatively small range of fuel to air ratios between the lower flammability limit and the upper flammability limit. The result is that it is not very easy to set fire to it, even if you are trying. You have to get fuel temperature, vapour pressure and ignition energy all within the right ranges.
Colin Bignell
The fact that it appears to have crashed, rather than making a hard but controlled landing suggests that it was not in auto rotation, hence my comment.
Exactly. It suggests some sort of catastrophic failure.
The AAIB are good, but not omniscient. There is a slight chance that they may never be able to say for certain.
Colin Bignell
Hum, IMHO if had "crashed" it would have gone straight through the roof in one hit. It doesn't appear to have done that, it rather hard and damaged the roof enough for it to then collapse a number of seconds later. The pub is also right next to the river, the pilot may have be trying to put ditch it there but didn't have suffcient control/time. You need a significant amount of height to switch a helicopter from powered to autogyro flight.
It does seem very odd for a twin engined helicopter to "just fall out of the sky". There has been very little reported from eye witness reports but I guess it was dark. Some mention of tail rotor failure and Eurocopter do have some what of a reputation when it comes to gearboxes...
Do these small civilian aircraft have data and voice recorders?
I heard someone (who sounded like he knew what he was talking about) on the radio say they don't have 'black' box recorders, but the engines do have some lower form of data recorders, also it would have radio contact with the police control room which would have call recording, as well at air traffic control.
They are not mandatory if the aircraft weighs less than 3000kg. However, some data is likely to be recoverable from the electronic systems. The previous Eurocopter gearbox problems have been cured by retro fitting parts AFAIK.
Well, if its wood, it tends to splinter and not always straight away. I'm not sure whether this is the question we should be asking though, more so, why do the Police as they were Saturday night around here, flying so low over a built up area for so long? One knows from all the progs on the Telly that they use thermal imaging and night vision devices etc, but one has always supposed that their twin engined craft were safe. OK its only one machine, but considering they are porbably all using similar craft, and as nobody knows the cause, it might have been prudent to at least ground them for a confidence check?
Brian
The occupants should have survived a controlled landing. It is reported as coming down fast and without the rotors turning.
Unless it was at the scene of an incident, which does not appear to be the case, I would expect the helicopter to have been near the river because it was flying along it. Rivers are usually helicopter routes through cities, because it minimises the risk to people on the ground if there is a failure.
If the tail rotor failed, then the response would be to put the helicopter into auto rotation, which removes the engine torque. That should not result in a crash like this.
This particular model does not, although there was a recent Airworthiness Directive, after cracks were found on a hub flange in France. SFAIK, only a couple of others have come down, one due to pilot error and one where the AAIB were unable to find any cause.
BBC reports say it is not thought this helicopter was fitted with a flight recorder. However, there would be both aviation and Police radios aboard. If they were not used, it suggests a very sudden event. If they were they would have been recorded and the recording passed to the AAIB.
Colin Bignell
Except if it had been a tail rotor failure, would it not have corkscrewed down rapidly?
The lack of damage to both main and tail rotors suggests neither was doing very much.
It is called progressive structural failure. One part fails, which increases the load on other parts. Ductile parts, such as steel bolts, may then slowly yield under the higher load before finally failing completely.
Colin Bignell
The engine automatically disconnects on power failure. It takes a significant amout of hieght to get sufficient speed on the rotor to make a soft landing, So if they were low they might not have had enough for a soft landing. The other possiblity is gearbox/rotor/transmission failure.
I understand the concept, but I was expecting the time interval to be short between one part failing and the next, milliseconds rather than seconds.
It was originally certified a few kg, 10kg iirc under the limit for FDR's, but lots of info can be retrieved from engine controls and navigation equipment.
A mark 1 eyeball is usually the most useful tool
Which bit of twin engined helicopter do you not understand?
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