With a jet, if you lose pressurisation, and (or especially if) you have passengers, you have to descend pretty quick. But then your fuel burn goes way up.
Is this required to be planned for and, if so, does anyone have the detail?
Peter wrote:
Is this required to be planned for and…
Not under the rules (EASA OPS) that are in effect around here. Would probably be the end of transatlantic flying.
You just have to hope it doesn’t happen. Only an issue over the ocean and mostly a single engine problem (with no redundant bleed air system).
In the PA-46 there is a squat switch failure which can prevent the aircraft pressurising. Many pilots crossing the atlantic pull the relevant breaker to prevent just this problem from occurring.
I was thinking of a window or a door blowing out, not a loss of pressure from an engine(s).
A jet will never hold any pressure if a window or a door is missing.
It’s an interesting point. Over land, probably not an issue because there are normally enough airports. Over the sea, everybody (except the pilots who have some 2hrs+ supply) might be dead by the time you land – even in a 4 engine jet.
JasonC wrote:
Only an issue over the ocean and mostly a single engine problem
Unfortunately not really. In my 4000something hours on pressurised aircraft I had one depressurisation (on the jet of course where it has the worst effect…) which was caused by a malfunctioning outflow valve. One moment it worked, the next one it was gone… These things are very complicated and delicate electro-pneumatic devices that are all bound to fail some day. After 1000 hours or after 10000 hours, but eventually they all break.
Covered in the new ETOPS, for multi with more than two engines. Twin jets need to be within 90 minutes (?), but three and four engines which have longer diversion sectors have to plan a de compression scenario, at least under Part 121.
Of course you have to descend in case of a rapid decompression. Terrain permitting to some level btw FL150 and FL 100. There you need oxygen for the pilots and also first aid oxygen for a certain percentage of passengers. IIRC the limitation for pilots’ oxygen was after the emergency descent during cruise at FL100 for 2 crew members for 105 minutes ( maybe it has changed in the last 10 years ). However you have to descend to FL120 or below once the passenger oxygen has been consumed and to 8000ft or below once the first aid oxygen (O2 bottles in the cabin ) is consumed.
On a long distance flight you most probably will have to divert.
There is in ICAO Annex 6 Part I what they call “additional fuel” which covers flight at a lower than planned altitude with higher fuel burn (due to loss of an engine or pressurization). As you know, Part I is for CAT. Part II doesn’t contain anything like it AFAIK. It’s up to you (if it’s in there, it’s masked as some general statement). It’s always interesting to see what it does to your range when you plan on crossing large stretches without airports close by to divert to (like oceans). AFAIK NAT manual doesn’t give additional requirements for this situation as far as fuel planning goes.
Peter wrote:
A jet will never hold any pressure if a window or a door is missing.
IIRC 747 is capable of maintaining pressurization with something like three or four windows missing. I think it’s a certification requirement (at least for the big machines).
Peter wrote:
A jet will never hold any pressure if a window or a door is missing.
Oh yes, it will, up to a point. The 747-100 (possibly also the -200) had a navigator’s window in the top of the flight deck which could be opened in flight (!) for celestial navigation. This whole issue was discussed ad nauseam in the pro section(s) of some fora following some of the recent depressurization events (e.g. the one in Greece, forget the airline now).
