AF 447 Search to resume (part2)

[Chris Scott]

THS Trim Tanks. CVRs & "Hot" Microphones.

Hi grity,
Just a reminder that the A300-600 series are of similar vintage to the A310. (They retain the A300 wing, if memory serves, unlike the super-critical A310 wing.) They have conventional flight controls, and (presumably) a traditional-size THS.

Tubby Linton will be able to explain more about the MAC figures involved. However, speaking generally about swept-wing, medium-to-long-range jet transports – those without trim tanks – the following may help. When pushing range towards the limit, the centre tank has a substantial amount of fuel at take-off. (You only put fuel in it if all the wing tanks are already full.) Because the centre-section is forward of the optimum CG, the aircraft is nose-heavy and inefficient until the centre tank is empty. So during the first few hours, the THS is in an inefficiently nose-up-trim position (i.e., having to generate more negative lift than later on). Having the THS trim tank full does not necessarily create an abnormally aft CG, but it can if the designers want it to.

EDIT (May 20)
The point I was trying to make above is that the A300-600R (and A310-300) trim tanks are unlikely to be used to create "relaxed stability": merely to offset the normal forward-CG problem that I have illustrated.
The A330/A340 are a different case, because of FBW. This is not to suggest, however, that they would be unflyable in Direct Law at cruising altitude. Current certification criteria would not permit such a regime, if my understanding is correct.

Garage Years,
Take the point about NR headsets, which I used from the early 1990s. Being short-haul, we had our headsets on nearly all the time. What I can tell you is that, when the cabin crew entered the cockpit, we had little difficulty hearing them and conversing. Admittedly, we often slid one earpiece off, but I'm not sure that was necessary. My understanding and experience was that it was steady "noise" that was almost eliminated: e.g., the 400Hz hum from the AC electrics, the airframe noise, and the engine noise.

I'd be surprised if "hot mikes" (for CVR recordings) were phased out on UK-registered aircraft as a result of noise-reduction headsets. Do we know if Air France CVRs use them?