Pressurisation when taxying?

[leonbrumsack]

Just a quick question...

I was recently onboard an aircraft which had to taxi to reposition from one part of the airport to another. However, I was a bit surprised that when the door was opened, there was a (slight) pressure change and my ears 'popped'. It was interesting to note that some crew members were covering their ears before the door was opened, so they obviously anticipated the pressure change. The taxi time was probably 8-10 minutes, and the equipment in question was a small jet aircraft.

Just wondering - is this 'normal'?

Thanks!

Leon

[Old Smokey]

Quite normal. Most aircraft pre-pressurise slightly on the ground, typically about 0.125 PSI Diff to keep the doors firmly in place.

[nitefiter]

some aircraft will pre-pressurise on the ground with engines running and all doors ect closed,normally to around -200 ft airfield altitude to avoid the cabin bump on take off.

[Flight Detent]

Hi Guys,

I don't agree, I thought that the only time the aircraft pre pressurizes on the ground is when the thrust levers are advanced for takeoff.

It's a reaction to the thrust lever position, as was mentioned, to stop the 'pressure bump' just after takeoff.

Though I need to mention that in all my time in B747 Classics, I didn't notice any 'bump' unless the FE was wrestling with manual pressurization - and we did "no bleed' takeoffs all the time!

The '74 Classic system holds the outflow valves full open until liftoff, great idea, regardless of air on or off, that way I know where they are all the time, in case of evacuation.

Cheers

[matkat]

Aircraft are not pressurised on the ground as quiete simply the cabin should be at ambient pressure,anyhow the cabin outflow valves are motorised open by the "weight on ground"switches thereby dumping any overpressure(i.e.more than ambient)the only way an aircraft should be pressurised on the ground would be for maintenance purposes and only essential personnel should be on board.In the case where the ambient pressure is higher than cabin pressure spring loaded -pressure relief valves are fitted in the fuselage to again produce an ambient pressure within the cabin.The only way I can think that the cabin would remain pressurised on the ground would be if the Cabin auto controller was U/S and the crew forgot to manually unpressurise the aircraft.

[BOAC]

737 will pressurize on the ground (at idle power - or on the APU) a few seconds after 'FLIGHT' is selected on the press'n ctrl panel and the main outflow valve has closed. Normal after start procedure. It would, however, possibly be sensible (if not contrary to SOPs of course:D ) to omit this step if just taxying to another stand.

[Flight Detent]

.........and what model B737 is that?

I don't think it is the later models (NG series).

Tks BOAC

[BOAC]

Sorry - should have said all the 737s with the 'old' panel ie with Flight/Ground switch, ie Classics excluding those fitted with DPCS.

AFAIK, all NGs have DPCS. Outflow valve is OPEN with weight on wheels unless power is high when it starts to pressurize.

We do not know which type of a/c Leon was in.

[matkat]

Good point Capt M. I am talking type specific B747 classics.

[leonbrumsack]

The aircraft in question was a Gulfstream V, and it was just to reposition from one stand to another.