Sunday, June 6, 2010

More enRoute Q and As

Photos Brian Losito (Air Canada)
Q: When a new aircraft is acquired, does it come with a warranty period similar to that of a new car? Jack Minacs, Markham, Ontario

An airplane’s “nose-to-tail” warranty is similar to a bumper-to-bumper car warranty in that most components are covered for a specified period, depending on the terms of the negotiated contract. Components such as engines, tires and brakes, which are all leased at Air Canada, come with their own warranties. But warranty or not, strict maintenance schedules based on hours flown and / or number of takeoffs and landings keep our aircraft in tip-top shape.

Q: Why do our ears get plugged upon descent, even though the cabin is pressurized? Christian-Marc Panneton, Québec

An aircraft’s cabin is pressurized to an equivalent of 6,000 to 8,000 feet above sea level at cruising altitude. As we descend, the cabin must depressurize – typically at 150 to 400 feet per minute compared to the aircraft’s descent rate of 1,500 to 2,000 feet per minute. For some passengers, the discomfort arises when the Eustachian tube, which equalizes the air pressure, is blocked. And if these tubes are tiny, as with babies, you’ll hear about it!

Q: What are all those dings heard when flying? Andrew Axson, Guelph, Ontario

The most frequent ding you’ll hear is the seat belt sign coming on or off. On Airbus aircraft, you’ll also hear a ding when the landing gear tucks into the belly. Other dings are heard when flight attendants at different stations use the interphone to communicate with each other, when the flight deck calls a flight attendant and when passengers press the assist button. And you may even hear cooking timers dinging in the galley.


Daniel said...

Would you hear the ones when sterile cockpit is in effect? Like in the Jungle Jet when they hit the sterile cockpit switch to the left of the Smoking sign, or does that one of the 3 lights displayed above the entrance to the cabin?

From the Flight Deck said...

Daniel. I can't speak for the Jungle Jet (Embraer) but the chime in the Airbus flight deck wakes up the dead. It's annoying. Airbus should have used a quieter chime for the cabin chime instead of using the same chime for SELCAL (Selective Calling). I'm certain it would be an easy modification. Again, the loud chime is distracting and sometimes you have to ask ATC to repeat things.

That was the problem of sleeping in the bunk of the A340 located directly behind the flight deck. The chime to flight deck could be heard inside the bunks.

Peter said...

A brief comment on why ears get plugged on descent. It has to do with anatomy. The eustachian tubes equalize pressure between the middle ear and the nasopharynx (the upper throat behind the nose). The part of the eustachian tubes that reach the nasopharynx protude slightly. Thus they aren't good at passively opening to let air in, which is necessary when descending as cabin air pressure increases. Rather, they are much better at passively allowing excess air to escape from the middle ear, such as during ascent when cabin air pressure is decreasing. By swallowing, some of the nasopharynx moves enough to permit the eustachian tubes to open. Yawning also works. Forcing air into the tubes (by pinching your nose, closing your mouth and squeezing your belly - a Valsalva manoeuvre) can overfill the tubes and damage your ear drum, or force phlegm with bacteria into the middle ear, leading to an ear infection.

Anonymous said...

Cool post, lots of good questions.

Also interesting on the Valsalva manoeuvre, I will try to avoid its use in the future.

From the Flight Deck said...

Peter. Thanks for the great explanation. Sounds like you have a medical background or a keen interest on how things work.

Again thanks for the comments.

Captain Doug

carlton said...

I remember flying back from Norway with a bad cold - the effects of the pressure and everything blocked up inside made me feel like my eye was about to pop out - very painful!

When I worked the cabins for KLM - we were always advised to call in sick if we had a cold due to the risk of bursting your ear drum in flight when the pressure in the eustachian tubes cannot equalize.

From the Flight Deck said...

Carlton. Head colds are taken pretty serious among crew. Just last month one Calgary based flight attendant booked off in Vancouver.
She seeked medical attention and had to remain in Vancouver for a couple of days in a hotel because of a head cold. Today's pressurization systems are much easier on the ears. Years ago we would get requests from flight attendants to descend earlier to lesson the descent rate.
Also passengers would open their suitcases only to find popped open containers such as toothpaste, creams, alcohol, etc. Some even claim their
glass covers to their watches popped off. Sure it still happens but less frequently.

Thanks for your comments.

Captain Doug

From the Flight Deck said...

Anon. Thanks for the feedback.

Captain Doug