Ask The Pilot

[lastrow]

When I board an aircraft the seats towards the front of the aircraft all seem to fill first and if there are vacancies my impression is that they are usually towards the rear. Having to move six passengers aft would appear to be fine tuning the aircraft trim. Is this always done? I had a recent flight when an A320 was replaced by an A321 because of increased passenger numbers. The curious thing was that about nine passengers were asked to report to the desk for a seat re allocation due to the change. Those who reported were from my observation regular people, none was over weight and a couple were quite small females. I have no idea where they were shifted to but surely nine average bodies out of a total of about two hundred would have negligible effect on aircraft trim. how are these calculations made and is fuel distribution used to compensate?

 

[jb747]

When I board an aircraft the seats towards the front of the aircraft all seem to fill first and if there are vacancies my impression is that they are usually towards the rear.

I regularly pax on a Saab 340, and on days when the loading is light, everyone is placed to the rear. All other things being equal, you’d probably load from near the CofG in both directions. But, they are never equal. you need to account for fuel, cargo, luggage...the weights of which can vary dramatically.

Having to move six passengers aft would appear to be fine tuning the aircraft trim. Is this always done? I had a recent flight when an A320 was replaced by an A321 because of increased passenger numbers. The curious thing was that about nine passengers were asked to report to the desk for a seat re allocation due to the change. Those who reported were from my observation regular people, none was over weight and a couple were quite small females. I have no idea where they were shifted to but surely nine average bodies out of a total of about two hundred would have negligible effect on aircraft trim.

There are many reasons that people might have been moved, but it is certainly possible that it was trim related. It is accounted for on a row by row basis in the cabin. Items below the floor have been weighed, and they are not placed in random positions. A load sheet is produced for every departure...ours arrive in the ACARs in the last minute or so before pushback.

how are these calculations made and is fuel distribution used to compensate?

It used to be a very complicated form, but like everything else these days, it is now computer generated. The final outcome must be correct for the entire flight. There is an allowed CofG range for take off, landing and cruise, and must account for the fact that we may burn about 40% of the aircraft’s take off weight before landing. In our case there is fuel in the tail at take off, and that will be moved in order to achieve a target. It will be gone when we land...and we never move fuel aft other than on the ground.

 

[Franky]

Hi JB747 - no doubt your'e counting down the days to your last flight before you join the group who are able to call every day Saturday. Thought I would share these pics with you, as you may well have flown in one or more of them during your Navy days. I guess you could say the achievements you have made can in part be put down to the good training you received at NAS Nowra.

 

[Franky]

Retirement is what you make of it, and I believe you are planning a Nullarbor drive in the future, which is as good a start as any. The contributions from you and the other pilot colleagues of yours to this forum has been outstanding, and I have really learnt from your collective experiences. Thank you and enjoy the retirement.
Franky

 

[jb747]

I’ve flown in many of the helicopters in the images, though the Sycamore and Scout are both before my time. Only ever went for one ride in an S2. The lone A4 in your sequence crashed before I arrived at Nowra.

 

[Quickstatus]

I came across a picture of the main landing gear of the A380 today. The rearmost wheel pair has white hubs compared with the ones forward of it which are dark.

Does the rearmost wheel pair have brakes?.

@jb747 do you anticipate needing the APU to power the aircon at takeoff on the SIN-LHR sector?

 

[straitman]

I’ve flown in many of the helicopters in the images, though the Sycamore and Scout are both before my time. Only ever went for one ride in an S2. The lone A4 in your sequence crashed before I arrived at Nowra.

JB.

You are making me feel old by retiring!

 

[jb747]

I came across a picture of the main landing gear of the A380 today. The rearmost wheel pair has white hubs compared with the ones forward of it which are dark.

Does the rearmost wheel pair have brakes?.

No, they don’t...

@jb747 do you anticipate needing the APU to power the aircon at takeoff on the SIN-LHR sector?

We rarely need to use APU bleed for a/c on takeoff. 24L in LA, when you have a tail wind and maximum weight is about the only time and place.

Singapore to London is about only 13:30, so our weight will probably be 50 or so tonnes under the maximum. It’s also a very long runway, so we’ll have plenty of performance.

 

[flyer89]

JB,

Whilst you can never know for sure do you think that if you had never entered the military you would’ve gone the GA route or Perhaps gone with a completely different profession entirely?

 

[jb747]

Whilst you can never know for sure do you think that if you had never entered the military you would’ve gone the GA route or Perhaps gone with a completely different profession entirely?

My initial interest was solely in military aircraft, so I suspect that if I hadn't been able to scratch that itch, I'd have gone in another direction.

 

[Captain Halliday]

I flew an A319-100 today OSL-LHR.

Prior to departure the captain made a PA advising we’d be de-icing before departure “as we picked up some ice on the way into Oslo”.

I was under the impression that pitot tubes, wings etc had anti-icing built in via some form of heating.

While I appreciate none of our current pilot contributors operate this type, or regularly fly in such conditions can you please describe how this would happen?

Where would this ice have likely been?

What features exist to prevent icing in flight?

How much ice can build up in flight before it becomes problematic?

 

[flychrisfly]

Hi Pilots, in Oz there seems to be peak periods of demand for (domestic) flights in particular Monday morning and Friday evening, especially in the golden triangle. Assuming there are more planes in the sky at these times, where are all these planes when not being utilised for the peak services? I appreciate that some would be allocated to the less businessy and more touristy routes but that wouldn't seem to accommodate them all. Thanks

 

[AviatorInsight]

I flew an A319-100 today OSL-LHR.

Prior to departure the captain made a PA advising we’d be de-icing before departure “as we picked up some ice on the way into Oslo”.

I was under the impression that pitot tubes, wings etc had anti-icing built in via some form of heating.

While I appreciate none of our current pilot contributors operate this type, or regularly fly in such conditions can you please describe how this would happen?

Where would this ice have likely been?

What features exist to prevent icing in flight?

How much ice can build up in flight before it becomes problematic?

The pitot tubes, AoA sensors, are electrically heated. I'd assume temperatures would be cold enough to warrant engine anti icing all the way into Oslo. Wing anti ice is a little different in that it's more of a de ice, ie, once ice accumulates then you use it. This can still be used on the ground after taxi in if needed though.

Deicing an aircraft applies to the fuselage, wings and tailplane so my guess is this is where they "picked up some ice on the way" in.

So to assist with removing ice in flight is engine anti ice (around the inlet), wing anti ice (on the leading edge), pitot tubes and AoA vanes are constantly heated throughout the flight. The two front windows and the two side windows are also heated for defogging and strength purposes.

The amount of ice that can build up depends on the amount of excess thrust the aircraft has to counteract the added weight of ice. It also disrupts airflow causing you to lose lift, compounded with the height at which you are flying at and the margin between high speed and low speed buffet (known as coffin corner).

 

[AviatorInsight]

During the middle of the day there's a lot of them also on the ground. We had 1.5hrs off in BNE after arriving in SYD, then another 1hr 20mins on the ground in MEL before returning to SYD. Like you mentioned, most of the leisure flights (BNK, CFS, AYQ, etc) all occur during the middle of the day.

 

[Quickstatus]

@AviatorInsight ,
If you have excess time between sectors where do you chill out?

 

[AviatorInsight]

@AviatorInsight ,
If you have excess time between sectors where do you chill out?

If the crew room is outside security it'll usually be a coffee shop until the next aircraft arrives.

 

[jb747]

I was under the impression that pitot tubes, wings etc had anti-icing built in via some form of heating.

While I appreciate none of our current pilot contributors operate this type, or regularly fly in such conditions can you please describe how this would happen?

Where would this ice have likely been?

What features exist to prevent icing in flight?

How much ice can build up in flight before it becomes problematic?

Funnily enough, I may have to deice tonight. Hopefully not, as London has never done this well. They don't get the conditions all that often, so they've simply never had to become good at it.

Most of the aircraft has zero icing protection. They're simply too big to have heaters everywhere, so only critical areas get some form of deicing or anti icing. Leading edges of wings can have a couple of different forms of deicing, but the larger aircraft generally use bleed air. Drain vents, probes, etc will have electric heating. Engines use bleed air, though they are so hot, it does seem counter intuitive for them to ice up at all.

Basically, no ice/snow at all is allowed on upper surfaces. The lower can have small areas of rime icing associated with cold fuel.

 

[AviatorInsight]

A photo from last night on the way back from CNS shows the Australian coastline with airports.

 

[jb747]

One of the effects of cold weather is that the fuel when loaded is also colder than usual. The fuel continually cools during the flight, but normally, even on very long flights, it doesn't get cold enough to become an issue. But, when it's cold to start with, you're likely to eventually get near to the 'cold fuel' limits. The fuel we'll be loading tonight has a freezing temperature of -37º (though out of the USA with a different mix, it's only -30º). As you can imagine, having the fuel freeze is a bad idea.

The different tanks on the aircraft cool down at different rates. Fairly predictably, small tanks in exposed extremities are the most affected. So, for the 380, the fuel out near the wing tips, and fuel in the tail will see the most cooling. Normally the tail fuel will be consumed/transferred forward, well before the temperature limits. The wing tip fuel on the other hand, is kept until quite late in the flight, as it used to reduce the bending loads on the wing. In fact, we normally take off with about 4 tonnes in each of those tanks, and the system automatically pumps them up to 8 tonnes once airborne. If the fuel becomes cold enough in flight, that same automatic system will give us a 'cold fuel' warning, and then pump the wing tip fuel into the main tanks.

Fuel in the large feed tanks is unlikely to cool enough to become problematic, though if it did, you'd have to descend to find some warmer air. Back when I was flying the 747, we had to descend on one flight from Hong Kong to London. I forget the exact number, but it was the coldest air I'd ever seen...so cold that it was right on the aircraft flight release. The very next day, the BA 777 that flew the same route had a double engine failure on approach to Heathrow...caused by the ultra cold fuel, and its interaction with some fuel filters.

 

[Quickstatus]

Does air temperature vary with altitude according to any formula/Rule of Thumb?. Like air pressure and altitude?