On a recent domestic flight here in the US, I had my TV screen turned onto the map view, showing our current position, altitude, and speed.
I was surprised to see that all the way down to 5,000 feet MSL, we were going about 330 mph (ground speed). Even crossing 10,000, we were closer to 400 mph.
After converting to knots, this is still much faster than the 250 KIAS maximum. What did the pilot or controllers need to do to make this allowable?
Air Asia A340 Flying Into London Stansted
The general rule in most airspace - pilots must reduce the speed to below 250 knots (287 mph) below 10,000 feet. This is to facilitate the work of the air traffic controllers, that is, to enable them to space out the incoming traffic evenly.
As far as pilots are concerned, we are happy to abide by this requirement as bird strike risks are generally higher at lower altitude. Lower speed means lesser risk of impact by birds on the windscreen or engines.
Having said that, this requirement can be changed subject to aircraft performance or at the air traffic controllers request.
However, if the pilot is not able to comply with this requirement, he must advise the controllers. For instance, when I fly the Airbus A340 out of London on a long haul flight, I take off at a very heavy weight and my safety (green dot) speed is around 275 knots during the climb below 10,000 feet. I either inform the controller of my limitation or just add this word “HEAVY” after my Call Sign, it would be understood that I would be climbing at a speed higher than normal
In your case where you were descending below 10,000 feet and the speed of your plane was higher than normal – I believe the controller was requesting the pilot to maintain a higher descent speed to facilitate his spacing with another aircraft too close behind him. So this higher speed is acceptable in such a scenario.
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