The answer to all our secrets
Warning Toxic!
Disgusted of Tunbridge
Disgusted of Tunbridge
Joined: Jan 2005
Posts: 4,011
Likes: 1
From: Hampshire, UK
With light taxi power set, it takes too long to accelerate to a proper taxi speed. I use a fair amount of power to get speed up to a decent figure and control with brakes from then on. You do not use differential brakes on big jets, and even differential power is not usually recommended. During taxi there is no set power- speed depends on weight, wind direction and taxiway slope. You just have to take it as it comes and keep on top of it.
Joined: May 2005
Posts: 203
Likes: 0
From: F370
Real Airplanes
In the real world,
It takes a little extra thrust to get rolling, but once you are moving idle is pretty much all you need. On a flat you may need brake to keep speed under control, but the only time I use extra thrust is going uphill or around a sharp corner.
From mostly flat airports,
Joe
It takes a little extra thrust to get rolling, but once you are moving idle is pretty much all you need. On a flat you may need brake to keep speed under control, but the only time I use extra thrust is going uphill or around a sharp corner.
From mostly flat airports,
Joe
Nemo Me Impune Lacessit
Joined: Jun 2004
Posts: 4,103
Likes: 5
From: Chabanais, France
The Boeing recommended way, for a light B757,767 and 747-400 is to get the aircraft moving and let it accelerate to no more than 20kts then firmly apply brakes and reduce to a fast walking pace, release the brakes and repeat. Am told it will minimise brake wear.
Mistrust in Management
Joined: Mar 2000
Posts: 986
Likes: 11
From: UK
Rainbow
You do not use differential brakes on big jets
Regards
Exeng
Joined: Sep 2007
Posts: 350
Likes: 0
From: Paris, France
Thanks for the replies. Looks like I'm safe setting the throttle to produce gradual acceleration and then tapping the brakes to slow down as required, if that's the way Boeing says to do it. I was worried about wear on the brakes or heating them up too much, but apparently that's not an issue.
I've not tried differential braking much because I figure it isn't used often in real life on large aircraft, and replies here seem to confirm that. It doesn't appear to have much effect in the sim unless I press one brake considerably harder than the other (in a small Baron, the aircraft will swing to one side with even the slightest differential pressure). I'll have to try the alternating technique and see how that works.
I suspect the throttle quadrant I have for my sim is a bit stiffer than the real throttle levers, and the range in which the throttles must be adjusted to go from slowing down to speeding up seems to be very small. Perhaps it's easier to make such small adjustments with the real throttles.
I haven't tried differential thrust at all (it's too hard to move the throttle levers separately in the sim), so I'm glad to hear that it isn't frequently used, as I was wondering about that as well.
Of the several aircraft I fly in the sim (737-800, 747-400, and 767-300ER), only the 767 seems to want to roll spontaneously at idle. The other two will eventually coast to a very gradual stop at idle thrust, depending on the weight of the aircraft and other stuff, of course. I'll have to try them all empty sometime to see what that does.
I've not tried differential braking much because I figure it isn't used often in real life on large aircraft, and replies here seem to confirm that. It doesn't appear to have much effect in the sim unless I press one brake considerably harder than the other (in a small Baron, the aircraft will swing to one side with even the slightest differential pressure). I'll have to try the alternating technique and see how that works.
I suspect the throttle quadrant I have for my sim is a bit stiffer than the real throttle levers, and the range in which the throttles must be adjusted to go from slowing down to speeding up seems to be very small. Perhaps it's easier to make such small adjustments with the real throttles.
I haven't tried differential thrust at all (it's too hard to move the throttle levers separately in the sim), so I'm glad to hear that it isn't frequently used, as I was wondering about that as well.
Of the several aircraft I fly in the sim (737-800, 747-400, and 767-300ER), only the 767 seems to want to roll spontaneously at idle. The other two will eventually coast to a very gradual stop at idle thrust, depending on the weight of the aircraft and other stuff, of course. I'll have to try them all empty sometime to see what that does.
Joined: Sep 2007
Posts: 49
Likes: 0
From: Toronto
Autoland Capability
I'm wondering if the autoland capability that most large transport jets have is really needed. How often are airplanes approaching their final destination that have visibilities of under half a mile? (maybe 1/20 flights?) So all those other times the system is not being used and creates a loss for the operator... And for all the other times that the plane IS landing in poor visibility why can't HUDs be installed and pilot lands the plane using the HUD this is a much chepaer than have an autoland system.
Joined: May 2000
Posts: 3,204
Likes: 2
From: Seattle
What makes you think a HUD is cheaper than an autoland system? What is the relative level of training and maintenance required for both? After all, the autopilot systems are already installed (2 or 3 for redundancy), and the integration into the autoland system is well understood. By contrast, HUDs are relatively new in the airline world, and certification is not a piece of cake...
Joined: Sep 2007
Posts: 49
Likes: 0
From: Toronto
i think its cheaper because mechanics and pilots have to constantly check if the EXTREMELY complex autoland system works, if it fails during low visibility - a diversion is needed, while in a HUD I'm quite sure that the system is much simpler since all it requires is to display primary display in another place (ie the HUD). I also don't think that the HUD system is new since a lot of old fighter jets already had that system and pilots coming from the military (back in those days) could have already known how to operate so the retraining would have been much cheaper for the operator, thus saving money once again.
Joined: Oct 2000
Posts: 8,266
Likes: 1
From: Berkshire, UK
So what would your proposed HUD display?? You still have to have the complex autoland equipment to get the aircraft on the ground.
With great respect, I don't think you fully appreciate the situation.. An HUD by itself cannot get the aircraft down in poor visibility - it's simply a way of displaying information to the pilot; a great deal of other equipment is required so an HUD cannot replace an autoland system.
With great respect, I don't think you fully appreciate the situation.. An HUD by itself cannot get the aircraft down in poor visibility - it's simply a way of displaying information to the pilot; a great deal of other equipment is required so an HUD cannot replace an autoland system.
Only half a speed-brake
Joined: Apr 2003
Posts: 4,459
Likes: 136
From: Commuting not home
Yes there would be. HUD merely enables the pilot to fly head-up and see instrument information while looking through the window at the same time. It doesn't solve the problem, of actually seeing what is in front of you. There is a formalised requirement that the minimium visibility for pilot to obtain sufficient visual reference of outside world so that s/he can correctly judge the aircraft position, velocity and trajecotry in order to land safely is 300 m. With a HUD and 200 m RVR, there still woul be no benefit. Autoland can solve this. Actually, have solved this 40 years ago.
Only half a speed-brake
Joined: Apr 2003
Posts: 4,459
Likes: 136
From: Commuting not home
I'm wondering if the autoland capability that most large transport jets have is really needed. How often are airplanes approaching their final destination that have visibilities of under half a mile? (maybe 1/20 flights?) So all those other times the system is not being used and creates a loss for the operator
Joined: Sep 2007
Posts: 350
Likes: 0
From: Paris, France
Talk of HUDs makes me thing of a question that has puzzled me for a long time: How do you keep the HUD aligned with the scene outside? I mean, if you are looking directly through the HUD, and the lines on the HUD match the contours of the runway ahead exactly, what happens if you move your head to one side? Don't the lines on the HUD shift out of alignment then?
Seems to me that either you'd need something to clamp your head in place relative to the combiner of the HUD, or the HUD would need some sort of optical system that somehow keeps the lines on the HUD in the right place no matter what the position or angle of your view through the combiner. So how is it done?
I'm not actually that keen on the idea of HUDs and I'm glad that they are not widely used.
Seems to me that either you'd need something to clamp your head in place relative to the combiner of the HUD, or the HUD would need some sort of optical system that somehow keeps the lines on the HUD in the right place no matter what the position or angle of your view through the combiner. So how is it done?
I'm not actually that keen on the idea of HUDs and I'm glad that they are not widely used.
Joined: Aug 2007
Posts: 96
Likes: 17
From: Bournemouth, UK
De-icing Question
I have been following the very interesting Iberia IB6166 BOS-MAD thread and it has prompted a SLF de-icing question.
A couple of winters back I was on a TOM 737 flight from BOH to CDG. It was middle of the day no frost and about +3c. While we were boarding it started raining. After boarding the capt announced there would be a 'short delay for de-icing', which was a bit of a surprise. The Ryanair next to us departed without de-icing.
As the sector from BOH-CDG is short it may be that the a/c didn't require fuel (at ambient) and as TRT was short from the previous arrival would the decision to de-ice in positive ambient temperatures and rain be based on the potential below 0c fuel temperature in the wing from the previous flight causing freezing on contact? If so how does the PIC make this judgement call as I assume it takes a long time for fuel temps to normalise to ambient field level temps that are only a few degrees above freezing?
A couple of winters back I was on a TOM 737 flight from BOH to CDG. It was middle of the day no frost and about +3c. While we were boarding it started raining. After boarding the capt announced there would be a 'short delay for de-icing', which was a bit of a surprise. The Ryanair next to us departed without de-icing.
As the sector from BOH-CDG is short it may be that the a/c didn't require fuel (at ambient) and as TRT was short from the previous arrival would the decision to de-ice in positive ambient temperatures and rain be based on the potential below 0c fuel temperature in the wing from the previous flight causing freezing on contact? If so how does the PIC make this judgement call as I assume it takes a long time for fuel temps to normalise to ambient field level temps that are only a few degrees above freezing?