Flybe/Dash400

[ianjlloyd]

I've just returned from a trip from Glasgow to Southampton with Flybe. There was an incident on the outward flight which concerned me and I would be grateful for any comments.

We took off from Glasgow and after 10 minutes or so the seat belt sign went off and my headphones went on. Shortly after I started thinking that the batteries in my headphones were needing replacing as i could hear a high pitched whining sound. I took the headphones off and realised that the noise was coming from inside the plane.

It was loud and at one stage a cabin crew member picked up the internal telephone and (I assume) called the flight deck and moved the handset to the area where the noise was coming from. The cabin crew were well aware that passengers were aware of and uncomfortable about the noise.

We landed without incident at Southampton and I am quite happy to accept that there was no safety issue. My query relates to the fact that at no time was any information given from the flight deck about the noise or its cause. I can appreciate that if there was a real issue, the first priority must be to ensure the safety of the plane - and its passengers. I don't think that this was the case here and as we left the plane (after delays caused by the non-appearance of Flybe groundstaff - the pilot seemed to be making a pre-flight inspection prior to the next departure.

Are there any suggestions as to what the noise might have been caused by and also what should the response of the flight crew have been? It was clear that they were informed of the noise. Presumably in pre 9/11 days one of them may have come to listen in person. I'm surprised that they did not make an announcement. All we had was approaching Southampton and the cabin crew ten minutes to landing message.

[Rob1975]

Hi Ian,

The -400 actually has a noise supression system, much like noise cancelling headsets, which creates vibrations to cancel out engine noise. Did the sound seem to come from within the aircraft?

Cheers,

Rob

[The Grim EPR]

People wiser than me will be along in a minute, but perhaps a slightly leaky door seal? The pressurisation will cope with a small leak, but it can make an odd noise.

Only a guess though.

[jabird]

In this sort of situation, I think it is a courtesy of the pilot to inform passengers, but there maybe all kinds of operational reasons why he didn't.

As you say, you all landed safely - yes, I'd point to the noise suppression system as the first culprit. The concept of the technology is to create alternative waves to cancel out those that a generated by the props. Not sure if we have any sound engineers here, but if that got out of synch, then suddenly 1-1=0 becomes 1+1=2.

[Di_Vosh]

I fly Dash8-300's and not Q400's, but they both have an ANVS (Active Noise and Vibration Suppression) system.

Occasionally they don't work (or don't work in certain parts of the cabin) but the sound described doesn't sound like a faulty ANVS.

In my airline (Aussie regional) there is no mandated PA that must be given in the situation described.

Perhaps there should have been some kind of PA, but if the crew didn't know what the cause of the sound was, they're not likely to make a PA saying "We don't know what it is", and the same would apply if they suspected that it was a dodgy seal letting air out.

My thoughts,

DIVOSH!

[ianjlloyd]

Thanks all.

I was sitting in row 3 and the noise did seem to be coming from the region of the front emergency exit although perhaps more from the area above the door than the door itself.

The noise started when we were in level flight (no idea how high) and stopped when we were reasonably well into the descent.

[Otto Throttle]

Whilst I can understand the desire for passengers to want to know the source of every strange noise heard on board an aircraft, unless there is a safety implication, then I see no reason for the pilots to make a PA. The exact nature and cause of the noise is not always obvious and so it becomes a matter of speculation, and I'm not in favour of providing passengers with spurious explanations based on guesswork. It can be more unhelpful than helpful. Take the example that made the papers a few years ago of the pilot "not qualified to land in fog"; a pilot trying to offer a well-meaning explanation to passengers for a weather diversion in terms they might understand and instead creating the opportunity for some mischief-maker to get their name in the papers with some twisted and sensational headline.

In way of an explanation for the original poster, I agree with those who point the finger at a door seal. These tend to produce high-pitched whistling or whining noises, whereas the noise suppression system has a tendency to either elevate the general level of engine noise in the cabin, or produce a knocking sound in the area of failed actuators.

Neither of these situations have an immediate safety implication, particularly if all cabin pressurisation indications are normal.

[Hotel Tango]

Yes, these are difficult situations, made more difficult with the sensationalisation culture that exists today. Nevertheless, although I don't dispute Otto's reasoning, one has to balance that with leaving pax uninformed and consequently perhaps (in some cases) a little distressed. In this particular case it was apparently obvious to the pax that the CC themselves were puzzled and in contact with the FD. Perhaps a few words of reassurance from the FD wouldn't have gone amiss. But I do agree with Otto that finding the right and satisfactory explanation can be challenging.