Ask The Pilot

[straitman]

I've seen a few photos of the coughpits of modern passenger jets, and I have a question about the controls... Obviously there are the autopilot, land and take-off buttons, what do all the others do?

Most of them are there so that the average person thinks that the pilot is really smart and can operate complicated equipment.

Some of us know better though.

 

[stewiejp]

How exactly does one weigh an A380/B747?

I owuld imagine the same way they weight B double/triple trucks - one small scale under each wheel and add up the weights.

 

[jb747]

I've seen a few photos of the coughpits of modern passenger jets, and I have a question about the controls... Obviously there are the autopilot, land and take-off buttons, what do all the others do?

Actually there isn't a 'take off' button. They are always manual, even if you intend engaging an autopilot as soon as you're airborne.

Over the years, the number of buttons has dramatically reduced. In a classic 747, there were (supposedly, I never counted them) around 900 buttons, switches and dials. But in the 747-400, that went down to around 200.

Looking around the coughpit....

The controls to actually fly the aircraft, yoke/joystick, throttles, rudder pedals and brakes, are simply located where they comfortably fall to hand. In front of the pilots are the instruments needed to know what the aircraft is doing, and where it is. In the centre of the forward panel, there's instrumentation for the engines.

Along the top of the forward panel (on the glare shield) are the controls for the autopilots. Not only do you have to engage the autopilot, but you have many ways of controlling just what it does.

The centre pedestal...the front part is where the FMCs reside. Between them are more systems displays (one screen but about twenty different display possibilities). The rear section of the pedestal has flaps, speed brake, rudder trim, and communications boxes.

Overhead...basically the controls for all of the systems. Fuel, hydraulics, electrics, air. In the normal course of events, you turn them on, and then leave them alone, but you need to be able to manage just what the systems are doing after any failures.

And then there's the big red button.....best left alone.

 

[jb747]

Most of them are there so that the average person thinks that the pilot is really smart and can operate complicated equipment.

Some of us know better though.

Back in the days when we could have visitors, a kid told me that we had the second best job in the world.

The best? Council worker!!!

 

[Kerrodt]

Hi JB,

Firstly, let me thank you for the tireless and unwavering effort you put into this thread. It is probably unmatched anywhere else in this forum, or any other forum.

This is my first question to you, well first two questions, but I have been an avid reader of this thread for some time.

1. I flew WLG -MEL on Wednesday on a QF 737. There was enormous wind at the airport and the aircraft was being tossed around even while sitting stationery at the gate, which caused delays, to the point that the pilot came on the PA and explained that part of the delay was that the wind movement on the aircraft was preventing the navigation system from being properly calibrated, and we couldn't leave until the wind steadied, the aircraft stopped moving, and the navigation system was allowed to calibrate.

The wind never stopped, but we eventually took off.

My question therefore is, what influence does wind have on calibrating the navigation system, and how does it get calibrated if the wind never steadies?

2. You have often quoted on here the concepts of "normal law" and "alternate law" (I think that's what the correct terms are that you use). I'm sure they are both very complicated, but could you give a brief outline of what each are, when they apply/don't apply etc.

Many thanks once again.

 

[jb747]

1. I flew WLG -MEL on Wednesday on a QF 737. There was enormous wind at the airport and the aircraft was being tossed around even while sitting stationery at the gate, which caused delays, to the point that the pilot came on the PA and explained that part of the delay was that the wind movement on the aircraft was preventing the navigation system from being properly calibrated, and we couldn't leave until the wind steadied, the aircraft stopped moving, and the navigation system was allowed to calibrate.

The wind never stopped, but we eventually took off.

My question therefore is, what influence does wind have on calibrating the navigation system, and how does it get calibrated if the wind never steadies?

The part of the navigation system that needs alignment is the inertial platform. Basically it needs to be very accurately levelled and aligned with true north. It is initially told where it is and quickly rough aligns itself. Then, knowing it is actually stationary, any movement that it measures it 'knows' is actually misalignment, so it keeps fine aligning until it is measuring zero movement. This process takes about nine minutes, and in the 737/767 can be the slowest part of the preflight. Obviously any real movement made by the aircraft destroys this process. It will try to work around it for a while, but if the movement persists it will eventually come up with a failure indication.

I've never seen one that didn't align due to wind, but I have seen a fair few alignment failures. Generally starting the process again (and only for the errant platform) will eventually get you over the hurdle.

2. You have often quoted on here the concepts of "normal law" and "alternate law" (I think that's what the correct terms are that you use). I'm sure they are both very complicated, but could you give a brief outline of what each are, when they apply/don't apply etc.

First thing to remember is that these laws only apply to 'fly by wire' aircraft (777/787, 320/330/340/350/380). Basically the aircraft don't have any natural feel, and can be quite unstable. The intent of the laws is to impose a set of rules that the computers will then use when making the aircraft flyable. Normal law is simply the Airbus law that is in use most of the time. Normal law includes various limitations, such as bank and pitch limits. It also imposes rules for overspeeds and stalling. When in normal law, you can basically fly the aircraft to the position you want, and then let go of the stick, and it will stay there. In some ways the behaviour in normal law is counter intuitive to many pilots, so it can take some learning. In normal law it shouldn't be possible to stall the aircraft.

Direct law removes all of the protections, and makes the aircraft behave as closely to a non FBW aircraft as possible. Effectively a 747 is ALWAYS in normal law (though of course, it doesn't really have laws). Alternate laws are a part way mark, in which some protections may still be valid, but not all.

There are a couple of other laws too. Flare law comes into effect at 100', and switches the aircraft to direct law in pitch, whilst remaining in normal law in roll and yaw. That exists because normal law would make the aircraft virtually impossible to correctly flare.

The laws that are discussed are basically Airbus. Boeing must have them, but for whatever reason, they don't get the attention that AB do.

 

[flychrisfly]

Hi JB

Is it my imagination or is it quicker to enter a turn (the period from level flight to the bank angle) than leave a turn (the period from tha bank angle to level flight)? Any reason for this?

Cheers

 

[jb747]

Is it my imagination or is it quicker to enter a turn (the period from level flight to the bank angle) than leave a turn (the period from tha bank angle to level flight)? Any reason for this?

There's no inherent reason that I can think of, and anyway, you'd be nowhere near the roll rate limits....only a small roll input is used, either by the autopilot or the pilot.

But...rolling out of a turn you're often aiming to roll out onto a specific track (i.e. an ILS), so the initial turn towards might be at 25º of bank, with that slowly being reduced as the heading and track converge on the ILS.

 

[mjt57]

Back in the days when we could have visitors, a kid told me that we had the second best job in the world.

The best? Council worker!!!

I reckon that you went from first best to second best. I read that Mac Tucker fellow's book recently. It must've really hurt having to step down from flying fast jets.

Having said that, if I was good enough to get into the airforce, I would've been content in flying rubber dog do out of Hong Kong, to quote a famous line...

 

[jb747]

I reckon that you went from first best to second best. I read that Mac Tucker fellow's book recently. It must've really hurt having to step down from flying fast jets.

Having said that, if I was good enough to get into the airforce, I would've been content in flying rubber dog do out of Hong Kong, to quote a famous line...

A large percentage of the guys who graduate from Pilots' Course don't want to fly fast jets. It's not for everyone, for a lot of reasons. Big aircraft, and helicopters all have their own sets of problems, and are attractive to many...

 

[Kerrodt]

Thanks for your response JB. Makes a lot of sense. Thank you. Greatly appreciated.

 

[petercr]

JB, I notice that last Monday there was a Q A388 flown from LHR-DXB-SYD as a charter flight (according to theqantassource). Do you have any knowledge of what it was about - surely that's a lot of (expensive) bums on seats for one very specific reason and I wonder why they didn't use a 744 (esp as it meant that the regular QF2 didn't run)...

 

[markis10]

JB, I notice that last Monday there was a Q A388 flown from LHR-DXB-SYD as a charter flight (according to theqantassource). Do you have any knowledge of what it was about - surely that's a lot of (expensive) bums on seats for one very specific reason and I wonder why they didn't use a 744 (esp as it meant that the regular QF2 didn't run)...

Its a religious group (the exclusive brethren) and it happens every year, I don't think QF have the 744s to spare now.

 

[jb747]

Its a religious group (the exclusive brethren) and it happens every year, I don't think QF have the 744s to spare now.

Correct. I don't think the economics would stack up with flying a 744 up there just for the charter. Commercial have plenty of warning and control the seat sales to take the charter into account.

I did one on the 747 a few years back. You couldn't ask for a more polite, or tidy, bunch of passengers.

 

[Flashback]

Its a religious group (the exclusive brethren) and it happens every year, I don't think QF have the 744s to spare now.

Freemasons?

 

[petercr]

Its a religious group (the exclusive brethren) and it happens every year, I don't think QF have the 744s to spare now.

Having read up on some of their beliefs it would have made for an interesting flight - all the men seated together and then women behind...

(and they apparently shun outsiders asking questions)

 

[spudseamus]

No TV ,no radio, no newspapers ! Sounds like an easy trip

 

[drross]

Freemasons?

No. Separate group altogether. Large communities in the USA and darling downs Of QLD and around in some Sydney suburbs as well. Lots of money. Their guru is an interesting business man.

 

[mjt57]

A large percentage of the guys who graduate from Pilots' Course don't want to fly fast jets. It's not for everyone, for a lot of reasons. Big aircraft, and helicopters all have their own sets of problems, and are attractive to many...

A few years ago I saw a special on TV about the RAAF's newest toy, the C117 transport.

They interviewed, amongst others, a young woman (rank of Wing Commander) who was one of the pilots of this aircraft. It looked like a lot of fun and some interesting airstrips that they would fly into.

I wonder if they got more flying time than the F18 guys, though. Like one pilot said, "its more about quality than quantity...".

 

[Boris spatsky]

Let's just say that the guys and gals who have all the operational experience since '99 are not the fast jet guys (excluding the three month Hornet deployment to wave the flag in Iraq in '03).