En Route PNR depressurised
 

Hi Anyone got a simple formula for calculating an en route, that's is while in flight, PNR that returns to the departure airport at 10,000ft due pressurisation failure at the PNR?

Cheers Mang

What type of aircraft are you talking about?

If you're operating a piston aircraft, where the Climb / Descent / Approach sector corrections are quite predictable, and over a short distance, say 200 to 300 miles where the mean wind would suffice, then the conventional formulae should be OK.

If you're operating a Jet aircraft, where the Climb / Descent / Approach sector corrections are highly variable with Weight / Temperature / Cruise Level, and over long distances (e.g. trans Pacific), and considerable wind variation can be expected, then the only safe way is Wind Zone by Wind Zone all the way out to the zone in which the PNR will lie, and apply the standard formulae within the zone.

If you want to apply the standard simplified formulae in the last case, it's suggested that you review your ditching drills and practice your swimming proficiency :eek:

Regards,

Old Smokey

filler up, kick the tires and go ....worry about reserves later when you really need them:ouch:

The computer flight plan supplies a C.P for two engine high level cruise. Low level return to adequate airport, in the critical fuel summaries. However this CP is based on using the minimum required fuel load for the flight. Increase the fuel load, which is the norm, and the C.P or in the case of a return to the departure airport, the PNR, and the PNR will now be further away from departure. Anyone have a simple formula for calculating this new PNR. Aircraft twin engine jet 737 / A320. Wind zones could be averaged for calculations.

Cheers Mang.

Time to PNR = (Endurance x GS home)/(GS out x GS home)

And just how are you going to calculate that Endurance when some of the flight is at Cruise Fuel Flow, and an unequal portion of it is going to be at the low level Depressurised Fuel Flow?:*

What you say works within limits for Normal Cruise Out and Normal Cruise Home, but NOT when 2 different sets of winds, and 2 different sets of Fuel Flows prevail.

Regards,

Old Smokey

Is this ETOPS? If not, you will always have a diversion within about 330nm of the return track. You can set off therefore, back to departure ?IF YOU MUST? and keep it under review once you know the fuel burn and winds at 10k. If it is ETOPS, your PLOG should have a fuel requirement for up to 120/180 mins at 10000 feet from which you can extrapolate an intelligent guess. Personally, I would, however, have thought that after a pressurisation failure you would want to land fairly soon?

Old Smokey, you are of course correct about the fuel flows. However I think the original poster is looking for a simple solution - which has been dealt with before and can be found at http://www.pprune.org/forums/archive...p/t-10820.html.
Gary Bristow also offers a solution based on the above formula in his book Encyclopaedia of Technical Aviation.
Lefty

Thanks Lefty, the link has helped and also using the standard PNR formula you suggest can be used to get a ball park to put into the FMC.
Cheers Mang.