Ask The Pilot

[straitman]

Prado + Swag = One of the best things in life

You have obviously not live in as many Army/RAAF camps around the place for as long as I have.

My reaction is exactly the opposite :!:

 

[mjt57]

You have obviously not live in as many Army/RAAF camps around the place for as long as I have.

My reaction is exactly the opposite :!:

Yes, for some it's an adventure, I s'pose. Like when I did the Marley Point Overnight Yacht race a few years ago. All these guys were loving staying up all night in the cold and the wet. Unfortunately, I wasn't as enthused, as it simply reminded me of doing a nightshift...

 

[flyingfan]

I did some searching but couldn't find something along these lines... do the pilots normally increase the speed of the aircraft as fuel is burnt off? I remember looking at the flight tracking screen on an SQ flight and as we approached the destination we seemed to increase speed from 800-something to 950 or so km/h, presumably as the aircraft became lighter a higher speed was possible in the speed/cost of fuel burn equation.

Another question - are autopilots set to/can be set to (very simply put) take the aircraft towards its intended direction with little or no 'manual' pilot flying after takeoff? I'm thinking of Varig Flight 254 - Wikipedia, the free encyclopedia where incorrect data seemed to guide the aircraft in the wrong direction, oblivious to the pilots.

 

[markis10]

Another question - are autopilots set to/can be set to (very simply put) take the aircraft towards its intended direction with little or no 'manual' pilot flying after takeoff? I'm thinking of Varig Flight 254 - Wikipedia, the free encyclopedia where incorrect data seemed to guide the aircraft in the wrong direction, oblivious to the pilots.

NZ901 is another example where the aircraft went in the wrong direction sadly.

 

[HarryB]

Another question - are autopilots set to/can be set to (very simply put) take the aircraft towards its intended direction with little or no 'manual' pilot flying after takeoff? I'm thinking of Varig Flight 254 - Wikipedia, the free encyclopedia where incorrect data seemed to guide the aircraft in the wrong direction, oblivious to the pilots.

We should wait for the expert opinion from JB of course, but I thought most modern commercial planes could be programmed to basically fly themselves and land themselves in some cases, albeit under close supervision from the crew. I think that was your question?

I would imagine the checking processes that should be in place would cover anything entered incorrectly into the FMC and these weren't followed on that particular flight. Such a simple shortcut with massive consequences. Something that struck me immediately was the relatively young age of the crew, and while it would be wrong to suggest that contributed to the accident it's easy to think they may have been a little more blasé than more senior pilots



Sent from my iPhone using AustFreqFly app

 

[serfty]

As far as I know, simplistically it goes like this¹:

• As fuel burns, total flying mass decreases.

• Being lighter, the aeroplane will climb higher.

• The higher the aeroplane travels the less dense is the surrounding air.

• The less dense the surrounding air, the less resistance/drag.

• The less resistance/drag the faster the aeroplane will travel.

¹ Facits such as applied power, pitch, etc. being equal.

[Edit]

This relates specifically to Airspeed​

[/Edit]

 

[markis10]

Keep in mind there are different speeds to be measured:

Airspeed - The speed at which the aircraft is passing through the air around it, be it indicated, calibrated, equivalent or true airspeed.
Groundspeed - The speed at which the aircraft is passing over the ground.

 

[flyingfan]

We should wait for the expert opinion from JB of course, but I thought most modern commercial planes could be programmed to basically fly themselves and land themselves in some cases, albeit under close supervision from the crew. I think that was your question?

Yes, my impression was that autopilots are used to basically keep the aircraft cruising and can autoland - I was interested in hearing about how automated the early part of the flight is.

As far as I know, it goes like this¹:

I'd like to know if the aircraft is permitted to increase speed in this way (under the watchful eyes of the pilots/autopilot) due to the laws of physics kicking in, or whether the pilots/autopilot go "okay we're 50 tons lighter, we can bump up the speed a notch now without too much of an impost on fuel economy," or some mixture of the two.

Not being technically minded for these matters I am grossly oversimplifying things.

 

[serfty]

...
Not being technically minded for these matters I am grossly oversimplifying things.

I did footy note 'most facits ... being equal' - i.e. with no change to control inputs such as throttle.

e.g. As the air become less dense, "Lift" decreases, but as the aircraft travels faster through the air this increases lift, so they counteract somewhat. If on autopilot, and the altitude is specifically set, as the aircraft gets lighter and starts to rise, the autopilot will generally reduce the throttle to compensate.

 

[Awesom Andy]

Generally, the airspeed does not change no matter how much fuel is carried. However, jet streams of up to 100mph are not uncommon, and this would definitely have an effect on ground speed.

In the most up-to-date systems, the autopilot can pretty much be turned on from just after take-off until the plane has landed. However, the plane cannot configure itself, i.e. you still need a pilot to raise/lower landing gear, raise/lower flaps, turn on auto-brake, arm spoilers, run through checklists, etc.

 

[loobloke]

Keeping velocity approximately constant, there is a specific lift:drag ratio which optimizes fuel consumption.
Have a look at: Step climb - Wikipedia, the free encyclopedia

 

[jb747]

In very simple terms, the airframe has a angle of attack which is its most efficient, and the engines have a power setting which is their most efficient. So, the aim is to climb to an altitude at which the power setting required for that AoA (speed) happens to be the engine's best setting. As the aircraft becomes lighter, the AoA for a given speed reduces, so the aircraft must SLOWED to regain that alpha (AoA).

Whilst using the same IAS at higher altitudes will give a higher TAS, the aircraft are operated at mach numbers above (roughly) FL280, so climbing higher normally results in a loss of speed.

The speed range available in the cruise is extremely narrow (in some cases only a couple of knots), but even in a normal situation, you can only go about .03 mach faster than normal.

If we really want to make up time you go low, down around FL280....which is why some of the regular flyers might have spent a fair bit of time going from Sydney to Melbourne, at that level. The fuel burn is unacceptable for a long haul flight though.

And back to the original question, a speed change of the magnitude you mention could only have been wind.

 

[HW]

JB

This is a great thread, I echo the sentiments of others thanking you for your time and effort answering questions. Many years ago you flew me on a 747 across the Pacific, at the time I knew of you as JB from the newsgroup AA. A couple of questions for you please:

When aircraft are towed by a tug from a remote parking stand to the gate in preparation for a flight, what systems are powered up (braking, APU etc)? What qualifications does the person sitting in the seat need while the tug is driving it to the gate? Is it just a mechanic who has been checked out on how to release/set the park brake?

In an earlier post you described how the numbers you call out on final approach are the winds off the nose (in cross wind and head wind components) - what system tells you what those numbers are?

You also described a Sim exercise that was set out of Dubai - why is this airport chosen, is it always at an airport where you might occassionally divert, or is the choice of airport arbitrary? Why wouldn't they set it out of Sydney or Melbourne for example?

I recently flew from Dubai to Singapore, as we were flying across Oman I happened to be looking outside the window at the very instance that another aircraft flew past in the opposite direction. Obviously since the crossing speed of the aircraft was quite large it was a momentary glimpse, however I was stunned that the aircraft was on the same flight level and appeared very close. Of course appearances can be deceiving when there is no other visual reference, but how close should an aircraft travelling in the opposing direction be, and is it unusual for airways to be shared like this?

 

[jb747]

This is a great thread, I echo the sentiments of others thanking you for your time and effort answering questions. Many years ago you flew me on a 747 across the Pacific, at the time I knew of you as JB from the newsgroup AA. A couple of questions for you please:

In its day, it was a good newsgroup. I guess a combination of time, and trolls, ultimately killed it off.

When aircraft are towed by a tug from a remote parking stand to the gate in preparation for a flight, what systems are powered up (braking, APU etc)? What qualifications does the person sitting in the seat need while the tug is driving it to the gate? Is it just a mechanic who has been checked out on how to release/set the park brake?

I don't know what their specific qualifications are. As far as I know, they are always engineers. Systems to be powered will differ with aircraft type. Normally, the APU is running, so electrical services are available. 747, a couple of the hydraulic systems (1 and 4 from memory) would enable braking and body gear steering. Airbus will handle them electrically. Accumulators on both types will enable some braking even if the aircraft is totally unpowered. You must not touch the brakes unless the tow bar breaks....the tug does all of the work.

In an earlier post you described how the numbers you call out on final approach are the winds off the nose (in cross wind and head wind components) - what system tells you what those numbers are?

In both types, the wind direction and speed is shown on the nav display. In the Boeings, the components are also dispayed on one of the FMC pages.

You also described a Sim exercise that was set out of Dubai - why is this airport chosen, is it always at an airport where you might occassionally divert, or is the choice of airport arbitrary? Why wouldn't they set it out of Sydney or Melbourne for example?

They move around. Melbourne and Sydney come up regularly. Recently, we've had HK, Dubai, Nadi, Noumea, Bali, Ontario, LA and London.

recently flew from Dubai to Singapore, as we were flying across Oman I happened to be looking outside the window at the very instance that another aircraft flew past in the opposite direction. Obviously since the crossing speed of the aircraft was quite large it was a momentary glimpse, however I was stunned that the aircraft was on the same flight level and appeared very close. Of course appearances can be deceiving when there is no other visual reference, but how close should an aircraft travelling in the opposing direction be, and is it unusual for airways to be shared like this?

From the cabin, you can't see most of the other aircraft, as the go exactly down the centreline. With the new RVSM rules there's 1000 feet between aircraft. From the 380, you can sometimes even hear the other traffic.

 

[markis10]

The passing aircraft was more than likely at 1000 ft above or below you as JB747 indicated, head to head you cannot use lateral or longitudinal separation, radar separation is normally 5nm (approx 9km).

 

[simongr]

Any chance you are flying to HKG today or from hKG on Friday?

 

[jb747]

Any chance you are flying to HKG today or from hKG on Friday?

Still on leave. I will be going to HK in a couple of weeks, but that's not much use to you I guess.

 

[docjames]

Out of interest, how long since you've last flown to HKG? Is it exciting or mundane to be heading there again?

 

[simongr]

No worries - enjoy your vacation I am fairly confident that the pilot will be ok . Also first flight in Nancy Bird Walton - the worlds most inspected aircraft

 

[jb747]

Out of interest, how long since you've last flown to HKG? Is it exciting or mundane to be heading there again?

June 09. HKG-MEL (QF30) was my last sector on the 744.

It's at the bottom of my 380 bids, because it's a short trip that starts and ends in Sydney. I flew there a lot on the 744 because the 29/30 was, I thought, the best way to go to London, and because the pattern started and ended in Melbourne.