Emergency descend versus driftdowncurve
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Emergency descend versus driftdowncurve
I have the following question:
We operate with a Fokker 50 over the Alps, where the MOCA is 14.000 true altitude. If during a decrompression you have to descend, my company came up with a rule to descend in 4 minutes to a pressure altitude of 13.000, to comply with the oxy-req. in the Jar-OPS. With this 4 minutes descend, you stay just above the driftdowncurve, according our flightdepartement.
My problem with this rule is that on a day with low QNH etc., you may end up 1200' below the applicable MOCA on that route, just to satisfy the 4 minutes oxy-rule and to stay above the driftdowncurve.
My question: How do other operaters fly with aircraft, not certified above 25.000', on routes where the MOCA is above the 13.000' pressure altitude.
Other question: I totally disagree with the rule that my company imposses on me, to reduce my rate of descend, so to be at 13.000 in exactly 4 minutes. (example: I fly at 23.000' and have to descend to 13.000', so my rate of descend is 2500' per minute. This means, with the power levers at flight idle, I have to increase the power again to stay at the barberpole. I am of the opinion that no matter what, you have to try to go down a.s.a.p., meaning power levers flight idle and max. rate of descend)
Please help me with a solution, because my flightdepartement is on the wrong track.
As a reference:
http://www.jaa.nl/jar/jar/jar/jar.ops.1.770.htm
(v) The oxygen supply requirements, as specified in Appendix 1, for aeroplanes not certificated to fly above 25 000 ft, may be reduced to the entire flight time between 10 000 ft and 13 000 ft cabin pressure altitudes for all required cabin crew members and for at least 10% of the passengers if, at all points along the route to be flown, the aeroplane is able to descend safely within 4 minutes to a cabin pressure altitude of 13 000 ft.
We operate with a Fokker 50 over the Alps, where the MOCA is 14.000 true altitude. If during a decrompression you have to descend, my company came up with a rule to descend in 4 minutes to a pressure altitude of 13.000, to comply with the oxy-req. in the Jar-OPS. With this 4 minutes descend, you stay just above the driftdowncurve, according our flightdepartement.
My problem with this rule is that on a day with low QNH etc., you may end up 1200' below the applicable MOCA on that route, just to satisfy the 4 minutes oxy-rule and to stay above the driftdowncurve.
My question: How do other operaters fly with aircraft, not certified above 25.000', on routes where the MOCA is above the 13.000' pressure altitude.
Other question: I totally disagree with the rule that my company imposses on me, to reduce my rate of descend, so to be at 13.000 in exactly 4 minutes. (example: I fly at 23.000' and have to descend to 13.000', so my rate of descend is 2500' per minute. This means, with the power levers at flight idle, I have to increase the power again to stay at the barberpole. I am of the opinion that no matter what, you have to try to go down a.s.a.p., meaning power levers flight idle and max. rate of descend)
Please help me with a solution, because my flightdepartement is on the wrong track.
As a reference:
http://www.jaa.nl/jar/jar/jar/jar.ops.1.770.htm
(v) The oxygen supply requirements, as specified in Appendix 1, for aeroplanes not certificated to fly above 25 000 ft, may be reduced to the entire flight time between 10 000 ft and 13 000 ft cabin pressure altitudes for all required cabin crew members and for at least 10% of the passengers if, at all points along the route to be flown, the aeroplane is able to descend safely within 4 minutes to a cabin pressure altitude of 13 000 ft.
