Ask The Pilot

[Mattg]

Between most destinations, there are laid down airways (i.e. there are about 6 parallel ones between LA and Hawaii). Aircraft all fly at about the same speed, so will tend to stay in whatever relative position they start out in. On some routes, free tracking is allowed, in which case companies can plan pretty well any route. Most of our flights across the Pacific fit into this system.

And, when you think about it, what is there to talk about? Gibberish (i.e. chatter) has no place on the radio, and beyond that, we all have the same tools available to us for handling weather, etc.

Thanks, I appreciate your insight

 

[@themrtd]

I have a question I hope you can help me with. Planning to Fly to the NYC shortly on Qantas. Can the Captain of the aircraft actually marry people like the captain of a ship can. If so, are Qantas like to be interested?

 

[jb747]

I have a question I hope you can help me with. Planning to Fly to the NYC shortly on Qantas. Can the Captain of the aircraft actually marry people like the captain of a ship can. If so, are Qantas like to be interested?

Sorry, but no...

 

[Tortuga]

Hey JB, when taking off I understand you need to reach a certain speed before the plane will leave the ground, how much is the calculation of this speed effected by the air density? EG. Taking off way above sea level.

When you mention the pitch of the aircraft, what is changing to effect it? I remember you saying +2 or +3 degrees is average for maintaining altitude on the A380??

 

[Dmac6345]

Hi JB, thank you kindly for all your fantastic answers on this thread. I have 2 questions regarding the strobes on Boeing and Airbus. Why does the Airbus have a double flash strobe and Boeing only 1. Also there are times when I have seen the Airbus with a single flash on the wing tip, but this is rare. Are there 2 different globes in each wing? Also why are the strobes switched on when crossing runways? Thanks in advance. Great job!

 

[jb747]

Hey JB, when taking off I understand you need to reach a certain speed before the plane will leave the ground, how much is the calculation of this speed effected by the air density? EG. Taking off way above sea level.

Quite dramatically. Basically you'll have less power, and will need to reach a higher TAS before achieving the needed indicated airspeed. Our calculations take it into effect, but because we select from a set of known runways, we don't actually have to enter the elevation, as that is already part of the data set for any given place. QNH and temperature are inputs. A one degree temperature change will have an effect of roughly 700 kgs, whilst 1 millibar will change things by about 600 kgs.

When you mention the pitch of the aircraft, what is changing to effect it? I remember you saying +2 or +3 degrees is average for maintaining altitude on the A380??

In a totally homogenous atmosphere, all that would be changing is the aircraft weight (which is reducing at about 220 kgs per minute). If you held exactly the same attitude as that weight reduced, the aircraft would slowly climb. So (assuming the power also stays the same) as the weight is reduced the attitude must very slowly come down. The total amount of change is probably less than half a degree...you certainly can't see it. But, if we left the engines at the same power, then the aircraft would also slowly accelerate...we don't want that either (in fact we want a slow reduction), so the power is also very slowly being reduced. It's really a constant balancing act, which autopilots and autothrottles do really well.

 

[jb747]

Hi JB, thank you kindly for all your fantastic answers on this thread. I have 2 questions regarding the strobes on Boeing and Airbus. Why does the Airbus have a double flash strobe and Boeing only 1. Also there are times when I have seen the Airbus with a single flash on the wing tip, but this is rare. Are there 2 different globes in each wing? Also why are the strobes switched on when crossing runways? Thanks in advance. Great job!

I don't think there is any particular reason for the Airbus/Boeing difference...perhaps as simple as different suppliers. It certainly makes picking the maker easy in pitch darkness.

The strobes are turned on crossing runways to make the aircraft a bit more obvious to any traffic taking off or landing. Whilst you'd be hard pressed not to notice a 380 crossing a runway in daylight, at night it is amazing how things can just disappear in the sea of lights.

 

[mjt57]

JB, just a comment, but I'm looking at the US on Flightradar24.com (tracking the missus' flight). When zoomed out it looks like a swam of flies or other insects attacking a plate of meat or something. Obviously it's a perceptive thing, given the size of the "aircraft" compared to the map. Even so, when zooming in around either LAX or JFK it seems to be extremely busy.

ATC and aircrew work very well together, I reckon, to avoid any "reportable" incidents...

 

[Walter_Plinge]

Can the Captain of the aircraft actually marry people like the captain of a ship can.

Off topic I know but to clear up a misconception the captain of a ship cannot legally marry people. The Marriage Act states who is able to do that: most ministers of religion and Commonwealth authorised celebrants.

 

[Blackbird]

But, if we left the engines at the same power, then the aircraft would also slowly accelerate...we don't want that either (in fact we want a slow reduction), so the power is also very slowly being reduced.

Just for clarification of the parentheses, as the aircraft gets lighter, we want a slow reduction in acceleration to maintain same speed or an actual reduction in speed?
I understand the need for less pitch and less power. Why do we want to go slightly slower?

 

[michaelidau]

In a totally homogenous atmosphere, all that would be changing is the aircraft weight (which is reducing at about 220 kgs per minute).

Possibly stating the obvious, but does this mean that a 380 engine averages around 55kg I found fuel per minute?

 

[jb747]

Just for clarification of the parentheses, as the aircraft gets lighter, we want a slow reduction in acceleration to maintain same speed or an actual reduction in speed?
I understand the need for less pitch and less power. Why do we want to go slightly slower?

As the aircraft becomes lighter, we decelerate to maintain the same angle of attack. A normal cruise will start at roughly .85. Over the next three or so hours that will reduce to .83. Then we climb to the next level, and go back to .85 and repeat the cycle.

If you happen to be held well below the altitude you want, the speed could be back as low at .76 or so.

Basically an airframe has a most efficient speed (or angle of attack). The engines also have a most efficient operating speed (which is somewhere around 85% thrust). So, you climb until the engines' most efficient thrust level happens to give you the airframe's desired speed. It is less inefficient to have the engines slightly off the correct speed than it is the airframe, which is why the engines are adjusted rather than the IAS as the weight changes, giving that slight reduction in cruise speed. And that explains why we step climb during flights...

 

[jb747]

Possibly stating the obvious, but does this mean that a 380 engine averages around 55kg I found fuel per minute?

Close enough for a steady state cruise....

 

[D747]

Basically an airframe has a most efficient speed (or angle of attack).

What is the optimum angle of attack for an A380 please jb?

 

[jb747]

What is the optimum angle of attack for an A380 please jb?

Dunno. It isn't displayed to us.

 

[Skyring]

Dunno. It isn't displayed to us.

I'm guessing that means:
A) the variations between optimum and non-optimum AoA are really small, and
B) the computer worries about it rather than the pilot.

In the old days, there would be movies of pilots cranking trim tabs around to get the aircraft balanced right - like after the Lancaster had dropped a load over the Ruhr - or pointing in the best direction if one of the engines wasn't quite healthy as the Connie lumbered over the Himalayas.

Are there still such things under the direct control of the pilot?

 

[Sprucegoose]

I don't think there is any particular reason for the Airbus/Boeing difference...perhaps as simple as different suppliers. It certainly makes picking the maker easy in pitch darkness.

The strobes are turned on crossing runways to make the aircraft a bit more obvious to any traffic taking off or landing. Whilst you'd be hard pressed not to notice a 380 crossing a runway in daylight, at night it is amazing how things can just disappear in the sea of lights.

The strobe sequence has always been different from a 727 to say 737 and airbus 320. When waiting for a particular aircraft at night we always could idenity it via strobe sequence. I used to do a lot of political driving work in Canberra a few moons ago.

 

[jb747]

I'm guessing that means:
A) the variations between optimum and non-optimum AoA are really small, and
B) the computer worries about it rather than the pilot.

Angle of attack changes are always small, unless you happen to be very slow. Flying alpha is quite a difficult technique, and it isn't used in the civil world at all as far as I know. It is used at low speeds by naval aviation...finals is flown on alpha.

In the old days, there would be movies of pilots cranking trim tabs around to get the aircraft balanced right - like after the Lancaster had dropped a load over the Ruhr - or pointing in the best direction if one of the engines wasn't quite healthy as the Connie lumbered over the Himalayas.

Are there still such things under the direct control of the pilot?

Trim still exists. There have always been many ways of handling trim...trim tabs, trimming (flying) tails, springs within the control runs, and many more. Trimming simply introduces a bias into the control system.

When the autopilots are engaged they normally look after pitch trim. In the Boeing the pilots can apply aileron trim, but it's rarely needed. Rudder is needed in both types in the engine out cases. The AB doesn't have aileron trim (which is a weakness). It looks after pitch trim itself as long as it is in normal or alternate law. In direct law you need to trim yourself.

Contrary to most of the myths, we still have full control of the aircraft. We most likely do things in different ways, but then that's always the case when comparing old and new.

 

[Dmac6345]

Hi JB,
I was reading in an article about Nancy Bird returning back home after her long stint in Singapore. I gather you have flown OQA after the repairs. Do you think that you can tell the difference before and after and are there any significant differences between any of the 380's?
Also I have had a few flights on QF 380's I'm the last 12 months and I was wondering if Richard D (Rdc) is still flying for QF and is flying A380's.
Cheers

 

[jb747]

I was reading in an article about Nancy Bird returning back home after her long stint in Singapore. I gather you have flown OQA after the repairs. Do you think that you can tell the difference before and after and are there any significant differences between any of the 380's?

No, you can't pick any differences. If anything, she's better behaved than before.

Also I have had a few flights on QF 380's I'm the last 12 months and I was wondering if Richard D (Rdc) is still flying for QF and is flying A380's.
Cheers

Rdc is still there.