Helicopter insty questions

[Lame Excuse]

Can any heli engineers tell me when the DFDR is powered up on a helicopter, and also what a split reading on a rotor/engine rpm indicator means? many thanks in advance

[Coriolis]

Don't know about DFDR (except it's a FLA* I've not seen before)
Needle split on Tacho just shows one bit's going but the other isn't (or is but at different speed)
As in..
Autorotation - rotor speed higher than engine ('cos it's rolled back or broke)
Engine started but clutch not engaged, so rotor not turning
Perhaps one freewheel on a twin slipping (would give slight upward split of slipping eng needle - not good, gearbox either poorly or pilot being very unkind!)

Hope it helps :)

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Ground tested, no fault found

[SeeNext]

If you mean the flight data recorder, the ones I'm familiar with are powered up as soon as electrical power is applied (external or internal) and the circuit breaker is made.

This allows it to record all of the engine start data - which is when a lot of the cock ups occur.

[400 Hertz]

Most North Sea helis use Combined Voice & Flight Data Recorders (CVFDR's). These are powered as soon as the bus goes live, when the pilot switches on power. They are stopped by inertia switches and floatation switches. The power required is only about 14 Watts.

Some aircraft use digital recorders which do the same job but are more expensive (£11,000 each). The most common N sea recorder is the Penny & Giles type 900D which uses tape.

IHUMS fitted aircraft take the same data stream that goes to the recorder and monitor it for exceedances in real time. This is ARINC 573 protocol but uses ARINC 717 sync words as well. Exceedances that do occour, allow the system to take a 'snapshot' of the data and save the info to a data card for later use by engineering staff.

IHUMS is fitted to all N Sea aircraft. There are some differences depending on weight of aircraft. Lighter (<5700 Kg) A/C require less params to be recorded (EUROCAE ED 55 spec).

It is possible for Pilots to erase the voice recording after flight, but they cannot erase the data recorded. On tape machines this is 5 hours of data, but digital recorders usually hold a lot more data, normally 10 hours.

Is that it?