Ask The Pilot

[Flashback]

I recall many years ago, friends who were aircrew on the BA 146 (same family as RJ85) said they often had head aches when operating these aircraft and some refused to fly in them. Some aircrews took industrial action. Seems the BA146 had bleed air and pressurisation issues, so, maybe the one you flew in was experiencing similar issues. Refer....www.aph.gov.au/binaries/senate/committee/rrat_ctte/.../report.pdf

That said, the modern airliners like the A380 and the B787 cabin air pressure is set at higher levels, making for a lower cabin altitude setting than earlier aircraft. Maybe it is just coincidence, but my long distance flights in the very quiet A380 (top deck) seem to get me to my destinations, some 22 hours later much better than older aircraft.

I'm guessing you mean the BAe 146?

 

[CaviAck]

I recall many years ago, friends who were aircrew on the BA 146 (same family as RJ85) said they often had head aches when operating these aircraft and some refused to fly in them. Some aircrews took industrial action. Seems the BA146 had bleed air and pressurisation issues, so, maybe the one you flew in was experiencing similar issues. Refer....www.aph.gov.au/binaries/senate/committee/rrat_ctte/.../report.pdf

That said, the modern airliners like the A380 and the B787 cabin air pressure is set at higher levels, making for a lower cabin altitude setting than earlier aircraft. Maybe it is just coincidence, but my long distance flights in the very quiet A380 (top deck) seem to get me to my destinations, some 22 hours later much better than older aircraft.

I flew on two different AF RJ85s and felt like cough both times but not in the sick or headache sense but in the grouchy I'm cramped get me the heck out of here way.

Yeah modern airliners can be pressurised to higher levels so the "cabin altitude" is lower making it a much more comfortable journey as there's more moisture and oxygen in the air.

The A320 has an extra inch of width for each seat vs the 737, so if you aren't very tall and are in the position to hog both arm rests, JQ can definitely be more comfortable.

You haven't sat in one of their seats in a long time have you? Might be wider but they're sure as heck not more comfortable.

 

[por930]

I'm guessing you mean the BAe 146?

Yes, BAe 146.....did not mean to specifically imply BA(British Airways) was the only carrier with these issues.

 

[andmiz]

There is a 'rumour' going around that Jetstar does not adjust the cabin pressure after take-off(until a lot later than other airlines) so that the oxygen levels are low and passengers nod off. Is this true? I know some people who flatly refuse to fly Jetstar because of this reason as it could be potentially dangerous if you are a frequent flyer.
Pretty much everyone I have asked has the same experience with Jetstar(nodding off during take off), but not some other airlines.

Absolutely ridiculous rumour.
However.....being a smoker, over weight, and under the influence of alcohol all increase your susceptibility to hypoxia. If you want to draw some conclusions then about Jetstar passengers.....

 

[Quickstatus]

turbulence

Hi JB747,
some inflight turbulence does not result in the flight deck switching on seat belt sign while other times seat belt sign is turned on in anticipation of turbulence.

Other than anticipated turbulence, at what point in the severity scale of turbulence is the SB sign turned on?


And Happy new year to all the pilots out there who endeavour to maintain a takeoff to landing ratio of 1.0

 

[samh004]

While a little discussion is good, as this thread is about asking the pilot I would like to draw your attention to the last paragraph of the first post of this thread:

As this is an "ask the pilot" thread, we ask that non-pilot members refrain from answering questions that have been directed to pilots until the pilots members have had a good opportunity to answer the question (i.e. at least 7 days).

Please try not to get too carried away in speculation before a pilot can respond to a question.

 

[straitman]

There is a 'rumour' going around that Jetstar does not adjust the cabin pressure after take-off(until a lot later than other airlines) so that the oxygen levels are low and passengers nod off. Is this true? I know some people who flatly refuse to fly Jetstar because of this reason as it could be potentially dangerous if you are a frequent flyer.
Pretty much everyone I have asked has the same experience with Jetstar(nodding off during take off), but not some other airlines.

Sounds like the crazies are winning if you believe this. An airline pilot maybe should comment here but I would expect that the cabin pressure adjusts automatically.

Absolutely ridiculous rumour.
However.....being a smoker, over weight, and under the influence of alcohol all increase your susceptibility to hypoxia. If you want to draw some conclusions then about Jetstar passengers.....

There are numerous things that change an individuals susceptibility to hypoxia and they are not all quantifiable.

A basic rule for flying is that up to 10,000 ft by day and 4,000 ft by night you don't need oxygen. (For airliners I'm talking cabin pressure)

You will however be in much better condition after 14 hrs at 3,000 ft (for example) than 14 hrs at 10,000 ft so the newer a/c that operate at a lower cabin pressure don't knock you around as much. Cabin humidity also comes into it as does an individuals' physiology.

Take for example La Paz Bolivia at 13,325 ft. Using conventional logic you would expect that all/most people would suffer from altitude sickness (hypoxia) and that the ill, the elderly, the overweight and/or the unfit would suffer more than the young, fit and healthy. In a general sense this is true however there are many exceptions where this is not the case and the fit athlete needs oxygen and the much less fit and maybe overweight does not. The same logic applies in a decompression chamber and/or in JQ's a/c, QF's a/c and all other a/c.

What I'm really trying to say is that hypoxia is one of those things that whilst the basic rules apply there are also many variations to those rules.

 

[jb747]

I thought I answered the pressurisation question on the previous page. ALL OF THE RUMOURS ARE UTTER RUBBISH.

These systems are always operated in automatic mode. They are a PITA to operate manually, and it will only be done as a result of system failures that force their operation as part of an ECAM/EICAS or emergency checklist.

Temperature can be controlled within a restricted range, and that can be delegated to the cabin crew systems on some aircraft. Even then the range is restricted, and it would be rare to see it out of the 21-26º range, (unless the system is operating in a degraded, averaging, mode).

The 787 does operate at a bigger differential pressure than older aircraft. This results in the cabin being about 700' lower at the cruise than in previous aircraft. The A380 operates at 8.7 psi, which if memory serves correctly, is exactly the same number that the 747 used. In any event, the cabin isn't much lower. To be honest, I think this is all marketing b/s. A larger differential will also make any depressurisation more interesting.

This is what two of the pages that show pressurisation data look like at various points in the cruise.....


The above page is the synoptic that is displayed about 99% of the time in the cruise. Note that it shows that cabin vertical speed is in Auto mode (and zero fps). The cabin altitude is also in auto, with the cabin at 5,800 feet. Differential pressure is 8.6 psi. Not shown on that page, but the actual altitude was 34,000 feet.





This page is the actual pressurisation synoptic. It's from much later in the flight, and the aircraft was now up at 40,000 feet. Differential has now gone to 8.7 psi (the max), with the cabin at 6,850 feet. Again, all of the control (for cabin alt, v/s, and the packs themselves) is automatic.

 

[Major]

I was just wondering approx. how many hours you guys logged in 2015 ?

 

[jb747]

Some inflight turbulence does not result in the flight deck switching on seat belt sign while other times seat belt sign is turned on in anticipation of turbulence.

If we turned it on every time that there was a bump, some flights would never have them turned off. Whilst getting cabin service is optional, sometimes going to the toilet isn't, so we try to keep some balance in the decisions.

'Anticipated' turbulence is a reaction to whatever we can see on the radar. As often as not, when we turn the signs on because the radar picture looks iffy, we'll also be taking headings to get around the bad bits. I suspect that's what 'teaches' some people that they can ignore the signs. Because we are successful at missing the stuff most of the time, they think it's unnecessary. Sometimes the difference between being totally thumped or totally smooth is a couple of hundred metres.

This is what a radar picture can look like. This cloud looks fairly benign...

Other than anticipated turbulence, at what point in the severity scale of turbulence is the SB sign turned on?

There's no magic number. If we feel it's bad enough, or if we get a call from the cabin, we'll turn it on.

 

[jb747]

I was just wondering approx. how many hours you guys logged in 2015 ?

845:50 for the calendar year.

 

[jb747]

I have seen many passengers change into PJs on Qantas flights in the premium cabins as soon as they get on the aircraft.

I know that many here do...but when paxing, as I'd rather not go down a slide into whatever is burning outside wearing the PJs, I prefer to wear my normal clothes, and especially my shoes, until later in the flight.

 

[RooFlyer]

In respect of cabin temperature, say on a QF 747 or A380 (but not only QF birds) , I sometimes think the J cabin is uncomfortably warm by mid cruise; I think that it's odd, as the temp would be regulated. Anyway, in those cases, if I notice others looking or mentioning same to their travelling companions, I might ask one of the crew to the effect "if others have mentioned it, could you check on the cabin temperature to see if its a bit warm" (ie not to ask them to do anything just for me ). I must say in your pic in post #8892, I would find temps of 23 or 25 degrees not comfortable for sleeping (but then, I'm a southerner).

More often than not, they will return a little while longer and agree the cabin was warm, and they've turned it down.

On Qantas 747s and A380s, is the temperature regulation delegated to cabin crew?
Is there a reason why the cabin might get noticeably warmer (mis-setting originally, or more laptops being used ...) or is it my imagination?
Do you think they would actually change some temperature setting (or request it, if not delegated), or are they just saying something to keep me happy? Sometimes I am sure I felt it getting cooler, but there's always the placebo effect, I guess ...

 

[jb747]

In respect of cabin temperature, say on a QF 747 or A380 (but not only QF birds) , I sometimes think the J cabin is uncomfortably warm by mid cruise; I think that it's odd, as the temp would be regulated. Anyway, in those cases, if I notice others looking or mentioning same to their travelling companions, I might ask one of the crew to the effect "if others have mentioned it, could you check on the cabin temperature to see if its a bit warm" (ie not to ask them to do anything just for me ). I must say in your pic in post #8892, I would find temps of 23 or 25 degrees not comfortable for sleeping (but then, I'm a southerner).

They are very big cabins, and the displays are showing a very small subset of the temperatures in them. The temps will differ with proximity to doors, crossovers, galleys, and across the aircraft from the sides to the middle. It's broken up in to a number of zones, with temp control limited to each zone. The ducting that services the cabins can only be broken down so far...it's not possible to give individual (or even close to it) temperature control. Whilst 25 is warm(ish), at anything less than about 23, some sections of the cabin will be complaining about the cold.

Most flights start with the cabin fairly warm, and the system is initially working to cool it. As the flight progresses, and the structure becomes colder, more heat is required.

More often than not, they will return a little while longer and agree the cabin was warm, and they've turned it down.

They've probably had a look at the displayed temperature, as well has simply having a walk to feel what it's like in other spots.

On Qantas 747s and A380s, is the temperature regulation delegated to cabin crew?

They are given limited control. The AB outright limits the range of temps that can be selected. The Boeing allows a small variation to the trim temperature set by the pilots. In both cases the cabin crew can only adjust by a limited range in either direction. The pilots can override, or resume control, if they want.

Is there a reason why the cabin might get noticeably warmer (mis-setting originally, or more laptops being used ...) or is it my imagination?

It's quite possible that it's a combination of both real and imagined. The actual average temperature of the zone may well be exactly the same, but, because the structure is getting colder (-20ºC or so), then the trim air temperature would have to be increased to keep that refrigerator effect at bay. Upshot is that the vent air that's cold on the ground will be warm in flight.

Do you think they would actually change some temperature setting (or request it, if not delegated), or are they just saying something to keep me happy? Sometimes I am sure I felt it getting cooler, but there's always the placebo effect, I guess ...

I expect that if they said they adjusted it, then they probably did. But, they can only adjust by one or two degrees. If you can feel that...I don't think I could.

 

[Awesom Andy]

I know that many here do...but when paxing, as I'd rather not go down a slide into whatever is burning outside wearing the PJs, I prefer to wear my normal clothes, and especially my shoes, until later in the flight.

Once, I was on a QF 747 where the FA suggested that I could change into PJs while everyone else is still boarding... (I declined getting changed early).

 

[RooFlyer]

They are very big cabins, and the displays are showing a very small subset of the temperatures in them.
<snip>.

Thanks again!

 

[ajd]

On a QFLink Dash 8-300 flight I had earlier today, our takeoff was delayed by a couple of minutes with engines running - the captain announced over the PA that we were burning off fuel for weight and performance reasons (it was a full flight). How often does this happen? We weren't held up for terribly long, so I assume they weren't burning off too much.

We then proceeded to do what I think the captain described as a "standing start" takeoff (my memory may be faulty) - we lined up on the runway and they applied power to the engines while keeping the brakes on, then released the brakes. How common is this, and under what circumstances would it be used?

 

[jb747]

On a QFLink Dash 8-300 flight I had earlier today, our takeoff was delayed by a couple of minutes with engines running - the captain announced over the PA that we were burning off fuel for weight and performance reasons (it was a full flight). How often does this happen? We weren't held up for terribly long, so I assume they weren't burning off too much.

Whilst I don't know exactly how the QLink guys work, I'll assume their system is similar to ours. Most performance data is now worked out using either an iPad or a laptop. This gives very exact answers for all of the performance calculations (literally down to the last metre and kilo). The aircraft displays are all digital, and they too give very exact answers. In the case you mentioned, I'd expect the wind was the deciding factor. If it has changed since the initial calculations, it could well put the aircraft over the performance limited weight. If that change is minor, then you'll need to burn off the extra. The max take off weight is measured at the start of the take off roll, so fuel burnt during the run isn't going to help you.

This issue comes up a lot on the A380. On many departures we need the maximum weight. We have to make a judgement call as to how much fuel we'll use for the APU (after fuelling is complete), and also to get from the gate to the runway. At LA, 25L could cost you 2,000 kgs whereas 24L will be about 600 kgs. So, before we line up we'll need to look at the weight and make sure it's below the max. If it isn't, we'll generally just have to wait for a few minutes (we're going through it at about 40 kgs per minute on the ground).

We then proceeded to do what I think the captain described as a "standing start" takeoff (my memory may be faulty) - we lined up on the runway and they applied power to the engines while keeping the brakes on, then released the brakes. How common is this, and under what circumstances would it be used?

I don't know what their rules might be. We never set high power on the big engines if not moving. There are all sorts of limits, but basically we don't get to full charge until about 70-80 knots. There is so much power that you'd be quite likely to damage the tarmac, and the aircraft would probably move...even with the brakes locked.

 

[smeacs]

Is the APU an on or off type of arrangement? or does it have a dynamic level of control depending on the power needs?

The initial thought I had was, can it consume different amounts of fuel on a different day in the same amount of time.

 

[jb747]

Is the APU an on or off type of arrangement? or does it have a dynamic level of control depending on the power needs?

The initial thought I had was, can it consume different amounts of fuel on a different day in the same amount of time.

We have no direct control over the APU, but you can control the loads to a degree. It will be running 2 generators, and air for the air conditioning. Leaving the aircraft connected to ground air, or power, will save you a bit of fuel. Not really enough to be of interest on one flight, but it would add up across the fleet over a year.

It looks after itself as the loads change.