The pilots should inform ATC when performing emergency descent, but, reporting a rapid descent, is it the same? Can you please, say some situations the pilots will report rapid descent?
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asked Jan 16 at 14:25
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2 Answers
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Well, an emergency descent is one where you're descending for safety and a rapid descent is one where you expedite a normal descent procedure. Another example to help differentiate between the two is an explosive decompression. The crew would initiate an "emergency descent" but if they suspect airframe damage they may consider maintaining the current speed and aircraft config to avoid further damage.
Goal of Emergency Descent: The goal is to descend as quickly as possible while remaining within the aeroplane's structural limitations. Not always rapid, requires an active emergency posing a threat to operations.
Goal of Rapid Descent: Aircraft descends at a much steeper rate than during a normal descent. This is usually done to quickly reach a lower altitude during emergency procedures but not always.
You are not going to not report either of them, both terms are usually used interchangeably but are not normal procedures either.
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Both are descents where you will do the following steps:
- Thrust levers idle.
- Autopilot to speed mode, and dial the speed bug to Vmo/Mmo, unless you suspect structural damage (such as from a frightening bang coming from the back), in which case you set the speed bug to current speed.
- If you have in-flight deployable speed brakes/spoilers that are good to operate at Vmo/Mmo, fully out to increase the descent rate.
If it's an emergency, like a cabin pressurization warning or smoke, you will be donning masks, setting the transponder to 7700, and declaring an emergency on the radio, which allows you to start down immediately and will have ATC clear the decks for you on the way down. Plus you will dial the ALT select on the autopilot to 10000 ft so it captures the altitude when you get there.
If it's not an emergency and you don't mind waiting, you'll be requesting a clearance for lower, perhaps asking for priority and explaining why, and you will leave the masks alone, or only have one crew member don one as a precaution (you might do this if a windshield crack appears, which is not uncommon, is usually on the outer lamination and benign, and you decide you don't need to go full ED but want to reduce pressure differential as fast as possible), and no transponder selection.
Also, if it's a non-emergency, you may avoid deploying flight spoilers/speed brakes or cranking up the speed to Vmo/Mmo, because the noise tends to scare the passengers.
