Any helicopter pilots/experts? Clutha Bar report.

I presume there are changes which could be made to prevent such mistakes being made, or prevent them causing a crash, but this is such an unusual occurrence that the issue hadn’t arisen before?

The report is very thorough, and lists every known case where the transfer pumps were erroneously turned off, but concludes that in all cases the circumstances were different to this one.

The specific recommendations made by the report are limited to recommending the installation of flight recorders, and to ensuring that the radio altimeter continues to work after loss of both engines, which might have improved the chances of a successful autorotation as there’s evidence to suggest that the pilot flared the autorotation too high above the ground.

Newer helicopters have pumps that can be run dry without harm. This removes the one legitimate cause for switching off a fuel transfer pump in flight, although the report seems skeptical about dry running being the reason for the pumps being switched off during the flight.

Auto-rotation, with the engines off you need to immediately lower the collective to maintain rotor speed. Once the rotor speed has decayed below a certain percentage of normal rpm then you are not getting it back and they will stop turning very quickly. That percentage might be 80-90% depending on type of helicopter so there is little margin for error.
AS the helicopter approaches the ground you raise the collective to flare for the landing. In all of this though you need forward airspeed, it won’t be able to hover.
It sounds like on this occasion the pilot misjudged his flare hight and ended up at 100 feet with no forward speed and the rotors stopped.

imnotverygood – Member

Err. How would that help. The FDR would tell you that the pumps were switched off, but not why. The CVR is hardly going to record him saying. “I’m just going to switch the pumps off because of x” unless he was in the habit of talking to himself

Correct FDR will provide pump status….if it’s one of the parameters recorded. CVR on the other hand would hopefully provide an insight into what was going on during the flight. It picks up not just speech of the pilot but all those onboard as well as ambient noises (engine/transmission sounds for example). I would expect one of the observers to be sat in the front assisting the pilot at times with checklists etc and I would expect that there would be conversation going on all the time rather than flying in deathly silence. Good crew resource management would dictate that the pilot would have appraised the crew of the low fuel warnings and communicated his intentions based on what he thought the situation was; just because the observers are not aircrew does not mean the pilot does not talk to them and tell them what is happening.

There is no guarantee that had there been a CVR fitted it would answer all the questions that remain, however it may have provided a much needed insight into the reasons for certain decisions.

Question for the experts… under what circumstances are the transfer pump switches required?
My car has a fuel pump (+ regulator and return), it’s essential at all times for the car to run, as I imagine they are in a helicopter, or not….?
When would you switch them off normally, or in an emergency situation?

Is it just for when a pump is faulty? any other reasons?

An aircraft has multiple fuel cells, the transfer pumps transfer fuel between these cells. There’s a few different configurations but that’s all technical wobble.

And depending on the configuration when/what/how/why/etc will dictate when the transfer pumps are turned on, or off. But that will all be laid down in the tech manuals and flight reference cards.

I’ve seen comments in other reports about the pumps being switched off because they’re running dry – presumably when fuel in main tank gets low and when flight manoeuvres result in fuel not sitting level in the tank – because running dry damages the pumps. Though as pdw says, the report seems to dismiss the idea that the pumps would have run dry.

When would you switch them off normally, or in an emergency situation?

Only if one of the pumps runs dry. As the main fuel tank becomes low, either the front or rear pump may become uncovered, depending on the pitch of the helicopter. In this case, you turn the affected pump off to stop it overheating, but you wouldn’t turn both off.

The report deemed that it was feasible that one of the two pumps would have run dry based on the fuel level and maneuvers being flown, but that a) the warning would have happened a few minutes after they calculated that the pumps were turned off and b) should have resulted in only one pump being turned off.

My car has a fuel pump (+ regulator and return), it’s essential at all times for the car to run, as I imagine they are in a helicopter, or not….?

If you’re interested, it’s worth reading the full AAIB report. It gives really quite a good explanation of how the system works.