UKH

The enquiry into this crash is currently news in Scotland.

Anyone understand helicopter fuel systems?

It seems the pilot has to pump fuel from a main tank into the two engines Supply tanks.

Question...

Why isn’t it one big tank like a car?

Why on something as sophisticated  as a helicopter doesn’t this all happen automatically?

https://assets.publishing.service.gov.uk/media/5669498c40f0b60369000004/AAR...

Redundancy. In case you get a leak in one. 

And I think the supply tank complexity is designed so that one engine runs out of fuel first rather than both at the same time. Supposed to make running out of fuel more survivable.

Could br that the smaller feeder tank provides a better and more reliable fuel feed into each engine and avoids any problems with cavitation or a pump being uncovered during manoeuvres. Why the crew switched off the transfer pumps is not clear. 

This seems to be at the heart of the matter. Sounds like they should be switched on at take-off and remain so for the duration. Is this the helicopter equivalent of forgetting to finish tying in?

That sort of makes sense but if the pumps from the main tank are alway keeping the supply tanks equally full won’t they both run dry at the same time... or are the supply tanks cunningly designed different sizes?

Reading the AAIB report it's a single supply tank, but partitioned near the bottom into two cells. Once the fuel level drops below the partition it then becomes two seperate systems. One of the cells is smaller than the other so the right hand engine fails first, giving a very big hint that the supply tank is really empty.

Before that happens there are multiple low fuel warnings, which were apparently acknowledged but ignored for some reason.

The following is interesting: “Seven of nine incident/accident reports between 1981 and 2014, involving the manufacturer’s helicopters, recorded the selection of both fuel transfer pumps to off as the primary cause of fuel starvation”. It hadn't happened on that particular model up to the crash, but it seems odd.

As there was no voice recording we'll probably never know what happened, but when the final report is published that will be as good as it gets.

7 out of 9 incidents/accidents have the same cause - it seems that a specific human error has been designed in.

I guess that raises the question of whether it's something to do with the helicopters themselves, or the recommended flying procedure for them. I know next to nothing about flying helicopters. It does seem odd.

Cheers. The 7 out of 9 thing is very interesting. That sounds like there is at least an element of bad design at play if the systems used are prone to user error. Like you say, it’s unlikely it will ever be fully understood why the pilot acted as it is thought he did.

I sort of understand now why one the bereaved relatives on the news was suggesting the pilot had been made a scapegoat. 

It does sound like there's an interface design problem involved somewhere.

The management of the centre of gravity of a helicopter is an important matter in flying the aircraft safely. Fuel is a major portion of the mass of most helicopters. Fuel sloshing around in a single tank is just not on, so it has to be managed. Micro-managed in some cases!

Wen you look at the 1994 Chinook crash on the W coast a few years back there is a lot of history of that.

They do say, with regard to twin-engined helicopters, that the purpose of the second engine is to fly you to the scene of the crash after the first engine fails.

Blimey, 25 years ago...

Although that was the RAF top brass desperately blaming the pilots, rather than an independent report (which cleared them).

My views on Chinooks can be summed up as 'never travel in an aircraft capable of having a mid air collision with itself'.

just shows how old I must be if it was "just a few years"!