Ask The Pilot

[jb747]

If a Boeing or Airbus is towed to a parking area for a number of hours before its next flight is the APU left running? If not, how is the aircraft powered up for flight?

Years ago the APU might have been left running, but now the fuel cost just adds up to way too much to do that.

Power can be provided from external sources, but for any long wait, the aircraft can just be powered down.

 

[dmitri]

jb, this may be a repeat question but I could't find it on here:

I fly a lot on the twin prop dash 8's on qantas link and 737's BNE-SYD. I find that the cabin pressure/ear-nasal cavity issue is much more noticable on the smaller planes. Is that directly related to the cabin size as I hardly have to do the "block nose and blow" method on the bigger planes.

thanks

 

[jb747]

I fly a lot on the twin prop dash 8's on qantas link and 737's BNE-SYD. I find that the cabin pressure/ear-nasal cavity issue is much more noticable on the smaller planes. Is that directly related to the cabin size as I hardly have to do the "block nose and blow" method on the bigger planes.

I don't know what program is used on the Dash 8s. I'll ask next time I get a chance (as I use them a fair bit these days too).

A reference I found on another forum (supposedly from a Dash 8 pilot):
The Dash 8 has a differential of 5.5psi. When cruising at 25,000', the Dash 8 can maintain a cabin altitude of 8,000'. When at 20,000', the cabin altitude will be 5,000'.

That would mean that even though the Dash is flying much lower than the jets, the cabin is as high, or perhaps even higher.

 

[Moody]

I was flying Brisbane to Sydney at twilight this week and was unusually in a window seat due to being flown ahead. I was admiring the view of the sun's dying light on the top of the clouds below us when suddenly a Jetstar flight screamed past going in the opposite direction. It made me reflect on how fast we were going, but also made me wonder whether there were conventions for Flight Levels on each route. For example SYD/BRI use FL35 but BRI/SYD use FL36.

Also is there any banter between flights crossing paths, or is it so commonplace that it is a "ships passing in the day/night" situation?

 

[dmitri]

I don't know what program is used on the Dash 8s. I'll ask next time I get a chance (as I use them a fair bit these days too).

A reference I found on another forum (supposedly from a Dash 8 pilot):
The Dash 8 has a differential of 5.5psi. When cruising at 25,000', the Dash 8 can maintain a cabin altitude of 8,000'. When at 20,000', the cabin altitude will be 5,000'.

That would mean that even though the Dash is flying much lower than the jets, the cabin is as high, or perhaps even higher.

cheers mate, thanks

 

[jb747]

I was flying Brisbane to Sydney at twilight this week and was unusually in a window seat due to being flown ahead. I was admiring the view of the sun's dying light on the top of the clouds below us when suddenly a Jetstar flight screamed past going in the opposite direction. It made me reflect on how fast we were going, but also made me wonder whether there were conventions for Flight Levels on each route. For example SYD/BRI use FL35 but BRI/SYD use FL36.

Also is there any banter between flights crossing paths, or is it so commonplace that it is a "ships passing in the day/night" situation?

There are a couple of conventions for altitude selection. Within Australia, the airspace is RVSM (reduced vertical separation), but basically the effect is that aircraft will come no closer than 1,000 feet for opposing traffic, or 2,000 if travelling in a similar direction.

Of course, most passengers don't expect to see other aircraft at all, so that 1,000 feet tends to become 'inches' in their minds. We actually see other aircraft all the time, and it's not uncommon to have a simultaneous pass of one a thousand feet higher, and another a thousand feet lower.

Separation between aircraft at the same altitude can be done by radar, distance, or time. The standards vary dynamically (by ATC), but 5 miles separation by radar is quite normal in the terminal phases of a flight.

 

[acoolbreeze]

Just curious as to the attraction (if any) of flying a freighter over a commercial jet?
I sometimes board the Atlas and CX flights and greet the crew in passing but never asked and they seem, rightly so, keen to get off and to their room I guess.
Are they youngish pilots racking up hours, or more experienced pilots content with their lot in life? Perhaps its more of a routine flying a freighter? (I could be wrong but I believe the CX flies a fixed route).
Thanks.

 

[jb747]

Just curious as to the attraction (if any) of flying a freighter over a commercial jet?
I sometimes board the Atlas and CX flights and greet the crew in passing but never asked and they seem, rightly so, keen to get off and to their room I guess.
Are they youngish pilots racking up hours, or more experienced pilots content with their lot in life? Perhaps its more of a routine flying a freighter? (I could be wrong but I believe the CX flies a fixed route).

The big freight outfits (Fedex, etc) provide perfectly good careers, with, perhaps, more variety than possible in the airlines. On the other hand, some pay virtually nothing, especially for FOs, and become simply a way station to more experience.

 

[Boris spatsky]

FEDEX and UPS in the US pay very well compared to the average mainline US airline pilot. If you like a lot of back of the clock flying and not having to deal with human passengers, then it can be a very rewarding career path.

I personally think the CX guys have it best - jumping between 744 and 748, pax and freighters. Good variety.

 

[jb747]

I personally think the CX guys have it best - jumping between 744 and 748, pax and freighters. Good variety.

I think you'll find that they (passengers/freight) aren't crewed by the same people .

 

[Boris spatsky]

My mate was 744 freighters, then went 744 pax, and just did 748 sim. Apparently they are now going to be rostered on both types as required (not sure whether one is limited to relief pilot only though?)

 

[Dmac6345]

jb747,

I witnessed an EK A380 taking off from Rwy 27 the other day at Melbourne. I must admit, I almost pulled over to check that I was wasn't sleep driving. I have seen a couple of QF A380's land on 27 but NEVER take off. Ever done this before ??

Also another question if I may,
Flying through turbulance is fairly common these days, and I find thayt the engines seem to be more active during this time. Is is because you guys are soring out a change in altitude, slowing down, speeding up etc? Do you reduce or increase the speed when the bumps appear?

Thanks again, for this incredible thread !!

 

[jb747]

I witnessed an EK A380 taking off from Rwy 27 the other day at Melbourne. I must admit, I almost pulled over to check that I was wasn't sleep driving. I have seen a couple of QF A380's land on 27 but NEVER take off. Ever done this before ??

Emirates operate the aircraft to NZ, so it would be quite light. I've used it once, on a flight to Singapore. The crosswind was beyond the limits on 16/34 (which is the only reason we'd use it). You can't get to LA or Dubai off that runway.

Flying through turbulance is fairly common these days, and I find that the engines seem to be more active during this time. Is is because you guys are soring out a change in altitude, slowing down, speeding up etc? Do you reduce or increase the speed when the bumps appear?

I think turbulence has always been pretty common....

In the cruise, most autothrust systems are slightly desensitised, so that they don't go chasing speed changes too aggressively. There's no need, and it burns more fuel.

There are a number of different forms of turbulence. The 'chop' that isn't associated with any cloud is called clear air turbulence. It's prevalent near the junction of two different air masses, so sometimes a quite minor altitude change can get you out of the area where they're mixing, into one or the other. Sometimes, though, it goes on for many thousands of feet vertically, and no amount of climbing or descending will get you out of it.

Turbulence associated with convective cloud is most easily avoided by simply not flying into that sort of cloud, which is what we do most of the time. Sometimes there's no option but to batten down and go through.

The aircraft in the cruise has a surprisingly limited speed range. Just after the point at which we climb to any given level, we may have as little as 10 knots margin on the slow side, and perhaps 20 on the fast side of our selected speed. If we get too slow, the drag will start to increase, and we may not have enough power to accelerate back, and conversely too fast and we run into the 'bricks'...the aircraft maximum speed limits. That's one reason why you don't normally try to climb over nasty weather...go high enough and you can actually have zero speed margin in either direction. Turbulence means the speed may randomly move in either direction, and the autothrust can be quite active (and will use large changes in power) to keep away from either limit. Sometimes it's actually better to descend and accept more bumps, simply to make the margins better. We don't normally change the target speed in turbulence, though if we happened to be near either of the limits (fast or slow) we might move the target to a more central position.

 

[Robbi]

jb, this may be a repeat question but I could't find it on here:

I fly a lot on the twin prop dash 8's on qantas link and 737's BNE-SYD. I find that the cabin pressure/ear-nasal cavity issue is much more noticable on the smaller planes. Is that directly related to the cabin size as I hardly have to do the "block nose and blow" method on the bigger planes.

thanks

I had two unpleasant J trips ADL-MEL and return last year (non-Dash 8) and both times I could not equalise my ears until well after landing. It felt like as soon as the flight reached the descent point the air pressure went back to sea level; I could hardly hear anything until I got to the terminal both times.

 

[jb747]

I had two unpleasant J trips ADL-MEL and return last year (non-Dash 8) and both times I could not equalise my ears until well after landing. It felt like as soon as the flight reached the descent point the air pressure went back to sea level; I could hardly hear anything until I got to the terminal both times.

Pressurisation doesn't work like that. Normally it climbs and descends between about 300 to 500 fpm. If at cruise you have approximately the maximum differential pressure, then it cannot exceed that...so basically the cabin descent rate has to be linear.

I'd suspect that you had some sort of cold or ear blockage.

As an aside...QF30's cabin hit a peak rate of climb of about 90,000 fpm.

 

[day-heg]

Talking of QF30, I'm studying for my ATPLs at the moment and have just done stuff on pressurisation, aircraft structures, oxygen systems etc, and they showed us that photo of you JB looking at a large hole in the side of your 747... this thread has been invaluable to put some of the stuff we are studying in to a more practical context and consider some of the answers you have given...
So, it's been said countless times already, but again - thanks JB!

 

[jb747]

My brother sent me a copy of that picture...and asked why I hadn't noticed the hole during the preflight. Good luck with the ATPLs.

 

[day-heg]

From what you said about your cabin altitude rising at circa 90,000fpm... I think I read you were at FL290 at the time of the incident and if your cabin altitude was about 7000ft (a guestimate), that suggests the decompression took about 15 seconds? Is that right? If so, that seems slow... certainly not 'explosive'? How big would the hole have had to be to be explosive?!?

 

[jb747]

From what you said about your cabin altitude rising at circa 90,000fpm... I think I read you were at FL290 at the time of the incident and if your cabin altitude was about 7000ft (a guestimate), that suggests the decompression took about 15 seconds? Is that right? If so, that seems slow... certainly not 'explosive'? How big would the hole have had to be to be explosive?!?

The cabin was at 3,700', and climbed to about 27,000'...which took about 15 seconds. That qualifies it as a rapid depressurisation. Explosive would require it to have taken place in less than 1.5 seconds (if I recall the definition correctly)....anything that could cause that would be unlikely to be survivable. Aloha may have qualified, but that flight was much lower.

The hole was about 2 square metres...but a 747 has a lot of internal volume.

Fighter aircraft normally have pressurisation that operates at about half of the aircraft altitude. The crew obviously wear protective gear all the time, but one reason for such high cabin altitudes is to minimise the effects of the loss of a canopy, which will certainly give an explosive decompression.

 

[mjt57]

Power can be provided from external sources, but for any long wait, the aircraft can just be powered down.

If powered down, as you term it, what's the sequence of events to get it to the point where you want to start an engine, or get the A/C going? Eg. How do you start the APU? And is it from there that other systems are started?

Oh, like your brother's comment about the hole in QF30. Does he fly too?

Finally, you talk about cruise speeds and low tolerance to speed change. I recall RdC telling a story in his book about a 747 which was flying at a rate which left no room for error, something happened and the crew had to take action to fix it.

I can't find the book to look it up, but would that be related to what you were saying earlier?