A bit of a riddle

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Working for FedEx, I recently found a post on the Flight Safety Bulletin board. A pilot had complained that a jumpseater (an employee hopping a ride on one of the cargo planes) had brought along a skydiving rig which "was equipped with a pyrotechnic device that could have gone off if the cabin had suddenly depressurized (cypress)." (If you have ever dealt with airline pilots you probably know that next to flying, their favorite activities are whining and bitching.) Anyway, the complaint he made was flawed for one reason and that is the riddle: What is the flaw?
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(sorry, I'm bored)

[OmriMon 0]

ummmm something about the fallrate of the plane and the altitude?
Free Skies,
Omri

[cyberskydive 0]

Besides the fact that if it was to go off the only thing hurt would probably be the rig owners wallet for the repack?
That maybe (guessing) depressurization alone would not set off the cypress??
D.Chisolm C-28534
webmaster@sunraydesigns.com
http://www.sunraydesigns.com

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You're on the right track. But I'm looking for specifics. It just struck me that the pilot was 'exactly' wrong.
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[cyberskydive 0]

OK- depressurization wont make it fire- casue it does that anyway in freefall(guessing again) and would only fire if the cabin was depressuruzed(so it wouldnt read falsly based on cabin pressure) and the fallrate was in firing range?
AND it had to be turned on and set properly?
D.Chisolm C-28534
webmaster@sunraydesigns.com
http://www.sunraydesigns.com

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Whether or not the Cypress had been "disabled" by "qualified personnel" prior to the flight was another concern of the pilot. But for the sake of this we can assume the Cypress was ON and functioning properly.
Obviously, the problem with the pilot's complaint has to do with him believing that sudden depressurization might have caused the Cypress to fire. But again his thought on the subject was "exactly" wrong (hint). You don't have to worry about thinking of speeds and altitudes. There is a basic principle the pilot was confused about.
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[Floater 0]

A Cypress is set off by an increase in pressure, not a decrease.

[Deleted 0]

Nice one!
If the cabin is depressurized the cypress should conclude from the air pressure that the jumper is rising instead of falling.
Blue ones
Dorothee

[flyboy62000 0]

Yeah, if the plane depressurized at cruising altitude the cabin altitude would go from about 7000ft to cruising altitude around 35000ft and there is no way the CYPRES would fire. It needs to decend rapidly through about 700-1200ft to fire.

[FallRate 0]

Exactly! I was a bit surprised that an airline pilot would make that error.
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[shermanator 4]

the square of the sum of the altitude and the velocity of the aircraft have to be equal to the drag and lift created in the vortex created by the planes disturbance of air molocules?

CLICK HERE! new blog posted 9/21/08
CSA #720

[nanook 1]

(slaps forehead) duuh!! The pressure has to increase not decrease.

that question threw me for a loop

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[aardvarkeater 0]

Also wouldn't the Cypress have to be turned on?

Muff Brother #4026
Loco Zapatos Rodriguez
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