Ask The Pilot

[andmiz]

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?

I spent a few years flying the Dash 8 prior to moving to the 747. It's likely that the at dispatch the payload figures given to the crew changed, once the crew had decided on a fuel figure. Surplus fuel loaded that was extra to all safety/legal requirements had to be burnt off (which for small amounts is far easier than de-fuelling the aircraft). Additionally, a standing start (in Bombardier terms called a Static Start) was used as it provides a few hundred kilos increase in regulated take-off weight when compared to a rolling start. It's only used when takeoff/initial-climb performance is otherwise an issue (as in this case) or when a specific dispatchable defect prohibits rolling starts.

 

[PaulST]

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.
.....

I'm curious to know how they can be that particular with such wide ranges of pax weights, especially on something like an A380 or 747. I was recently on an A330 with a hundred (or so) Scouts so I suspect that the aircraft could have weight many tonnes less than a flight full of adults.
Is there an average weight they make the calculations with?

 

[Hvr]

I'm curious to know how they can be that particular with such wide ranges of pax weights, especially on something like an A380 or 747. I was recently on an A330 with a hundred (or so) Scouts so I suspect that the aircraft could have weight many tonnes less than a flight full of adults.
Is there an average weight they make the calculations with?

Well they knew who they were so they could be prepared. I also imagine they have a guide as to the number of adults and children on board.

 

[PaulST]

Well they knew who they were so they could be prepared. I also imagine they have a guide as to the number of adults and children on board.

True and my example was probably fairly extreme. There's a huge variation within adults though, with a thin short guy weighting ~70kgs while a former rugby player could easily be another 50kgs.

 

[DrA]

This may be nothing...But I just had a very odd flight from BNE to TSV. Shortly after take-off, the plane kept banking from side to side the entire way up the coast, basically in a zig-zag type pattern the whole way up. I was watching it out of the window. Would that potentially be the pilot trying to avoid turbulence? And if so, wouldn't it have just been better to go around it rather than playing dodgeball so to speak?

 

[Captain Halliday]

This may be nothing...But I just had a very odd flight from BNE to TSV. Shortly after take-off, the plane kept banking from side to side the entire way up the coast, basically in a zig-zag type pattern the whole way up. I was watching it out of the window. Would that potentially be the pilot trying to avoid turbulence? And if so, wouldn't it have just been better to go around it rather than playing dodgeball so to speak?

What was the flight number? That would allow one of our contributing pilots to look at a track map.

 

[DrA]

What was the flight number? That would allow one of our contributing pilots to look at a track map.

Flight number: QF974

You can kind of see it on Flightaware.

 

[andmiz]

This may be nothing...But I just had a very odd flight from BNE to TSV. Shortly after take-off, the plane kept banking from side to side the entire way up the coast, basically in a zig-zag type pattern the whole way up. I was watching it out of the window. Would that potentially be the pilot trying to avoid turbulence? And if so, wouldn't it have just been better to go around it rather than playing dodgeball so to speak?

There's been rain moving through the coast between TSV and BNE all day; isolated embedded thunderstorms up to 35,000 feet and turbulence between 12,000 and 25,000 feet. Likely just storm dodging and given the large size of the area forecast, likely better to pick their way through rather than divert the entire way around. The flight aware plot shows a bit of manoeuvring off their flight planned route; most of which just south of Mackay. Just a matter of course this time of the year in Mid/North Queensland.

 

[DrA]

There's been rain moving through the coast between TSV and BNE all day; isolated embedded thunderstorms up to 35,000 feet and turbulence between 12,000 and 25,000 feet. Likely just storm dodging and given the large size of the area forecast, likely better to pick their way through rather than divert the entire way around. The flight aware plot shows a bit of manoeuvring off their flight planned route; most of which just south of Mackay. Just a matter of course this time of the year in Mid/North Queensland.

I thought it might be something like this, but I fly this route pretty regularly, and it's the first time I've ever seen the plane do this. My experience is that they normally just change elevation or fly through it and tell us to buckle up, not play dodgeball. Was just curious

 

[Mattg]

I've noticed that on 5-abreast aircraft (Boeing 717, MD80, some of the early Boeing 737-100s, etc.) the seats always seem to be in a 2-3 configuration, i.e. with 2 seats on the left hand side and 3 seats on the right (facing the front of the plane). Is there any reason from an aerodynamic perspective for this? Or is it simply convention?

 

[jb747]

I thought it might be something like this, but I fly this route pretty regularly, and it's the first time I've ever seen the plane do this. My experience is that they normally just change elevation or fly through it and tell us to buckle up, not play dodgeball. Was just curious

You can't normally fly over convective clouds. You may be able to climb over a layer of turbulence. Going around the weather may not actually be possible. It often extends for hundreds of miles. But, the nasty bits are normally smaller, and you can pick your way through them. If you didn't thumped, it sounds like they did it right.

Going through...you've not really been through any nasty stuff. Very few people have.

 

[jb747]

I've noticed that on 5-abreast aircraft (Boeing 717, MD80, some of the early Boeing 737-100s, etc.) the seats always seem to be in a 2-3 configuration, i.e. with 2 seats on the left hand side and 3 seats on the right (facing the front of the plane). Is there any reason from an aerodynamic perspective for this? Or is it simply convention?

Just the makers choice. Aerodynamically the aircraft wouldn't care.

 

[jb747]

I'm curious to know how they can be that particular with such wide ranges of pax weights, especially on something like an A380 or 747. I was recently on an A330 with a hundred (or so) Scouts so I suspect that the aircraft could have weight many tonnes less than a flight full of adults.
Is there an average weight they make the calculations with?

If the pilots make a last minute change, then that's based on a standard number...but, there's very little change allowed. Averages are used by load control, but they use numbers that are updated every now and then, and which try to account for most factors. Over the loads we're talking about, any variation makes up a tiny percentage of the final weight of the aircraft. Even the 500 passengers on a 380 only amount to about 10% of its take of weight....

We're probably using numbers to a greater precision than they are measured, but that's the nature of the beast.

 

[flychrisfly]

When selecting various degrees of flaps during the periods when they are not fully retracted, do the controls automatically adjust the slats too? Can flaps and slats be controlled separately if required? When might this happen?

thanks!

 

[docjames]

On the topic of fuel saving over a fleet year (vs the tiny saving on one flight), after landing a 4 engine aircraft, why aren't 2 engines shut down after exiting the runway (to save fuel)? Or are they and pax just don't notice?

I guess it could equally apply to 2 engine aircraft (shut down 1) but the asymmetric thrust I guess would be a reason? Again, possible but perhaps not a good idea? I vaguely recall US airlines taxiing on one engine during long ground delays at JFK, ORD etc. so i assume technically it can be done but presumably engine warm-up times etc are part of the equation. So, leading from that, how long between "engine start up" and "commence takeoff roll" is required (akin to "gunning" a cold car motor I guess)? And similarly, does there need to be a "cool down" time after landing (again i'm sure "immediately" is possible but there is perhaps a maintenance tradeoff akin to the derate takeoffs meaning a preferred minimum time from flight to shutdown?)

Thanks (and sorry for asking multiple questions in one post!).

 

[TomVexille]

I've noticed that on 5-abreast aircraft (Boeing 717, MD80, some of the early Boeing 737-100s, etc.) the seats always seem to be in a 2-3 configuration, i.e. with 2 seats on the left hand side and 3 seats on the right (facing the front of the plane). Is there any reason from an aerodynamic perspective for this? Or is it simply convention?

I'd suggest convention, as DL have a 3-2 configuration on some aircraft

McDonnell Douglas MD-88 : Delta Air Lines

 

[ajd]

I'm curious to know how they can be that particular with such wide ranges of pax weights, especially on something like an A380 or 747. I was recently on an A330 with a hundred (or so) Scouts so I suspect that the aircraft could have weight many tonnes less than a flight full of adults.
Is there an average weight they make the calculations with?

Occasionally this can be problematic... http://atsb.gov.au/media/5092920/ao-2014-088_final.pdf

 

[CaviAck]

Occasionally this can be problematic... http://atsb.gov.au/media/5092920/ao-2014-088_final.pdf

What's interesting from that is if an adult is taken to be 87kg and I assume that's including cabin luggage, I'm 23-25kg heavier than that, or a staggering 26.4-28.7% over! Might not be an issue on big jets but how is that going to affect smaller aircraft like CRJs, Dash 8s and ATRs?

 

[jb747]

What's interesting from that is if an adult is taken to be 87kg and I assume that's including cabin luggage, I'm 23-25kg heavier than that, or a staggering 26.4-28.7% over! Might not be an issue on big jets but how is that going to affect smaller aircraft like CRJs, Dash 8s and ATRs?

You'll have to buy two seats, and they'll divide your weight by two.

 

[jb747]

On the topic of fuel saving over a fleet year (vs the tiny saving on one flight), after landing a 4 engine aircraft, why aren't 2 engines shut down after exiting the runway (to save fuel)? Or are they and pax just don't notice?

We do, but there are a number of riders. Firstly, there are always time limits between the landing and shutdown. Normally about 5 minutes, and 90% of the time we've got the 380 parked within a minute or so of that time. Also, it affects the ability to do tight turns, and can increase jet blast, so you'll need to consider the taxi route, and especially the final turn on to the bay.

I guess it could equally apply to 2 engine aircraft (shut down 1) but the asymmetric thrust I guess would be a reason? Again, possible but perhaps not a good idea? I vaguely recall US airlines taxiing on one engine during long ground delays at JFK, ORD etc. so i assume technically it can be done but presumably engine warm-up times etc are part of the equation. So, leading from that, how long between "engine start up" and "commence takeoff roll" is required (akin to "gunning" a cold car motor I guess)? And similarly, does there need to be a "cool down" time after landing (again i'm sure "immediately" is possible but there is perhaps a maintenance tradeoff akin to the derate takeoffs meaning a preferred minimum time from flight to shutdown?)

One consideration for starting on the roll is that of fire protection. That's the time that you'll get a tail pipe fire, and with nobody to advise you or to fight it, things might become a bit tricky. There are time limits at both ends of the operation. 380 is 5 minutes after landing. Oil temperature is also a limitation before application of power. It's never an issue if the engine has been running from the gate, but potentially would become one with a later start.