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NotaLOT
3rd Feb 2010, 12:23
Hello All,

I am a long-time reader of Pprune, but this will be my first contribution.


I am currently involved in analysing runway exit and in particular RET locations for a runway.


I would like to get the pilot's perspective on the subject, especially for Code C aircraft, and in particular on these issues:

1) At what speed can you feasibily turn off into a 90 degree exit? What parameters of the exit impact on the exit speed, the width, the length, markings, knowledge of the airfield, visibility?

2) If a runway has a RET that is designed to handle aircraft at speeds up to 30 knots, will you actually endevour to use it at that speed? What factors affect your exit speed on a RET?

3) And this is particularly for A320/B737 pilots, how likely are you to be able to use a 30 knot RET located at 1500m from the threshold. I understand this is a very vague question, since there are so many factors that affect your braking performance, but some kind of general feeling on the matter would be very much appreciated, perhaps based on your experience at airports you fly to.

Thanks in advance for any useful info.

BOAC
3rd Feb 2010, 13:29
Not an option for 737: to stop in around 1200m would require mucho braking. While it would work some of the time, it would not be reliable for planning for runway utilisation.

MD83FO
3rd Feb 2010, 15:05
our company has an sop limited 90 degree turning speed of 10kt (strictly monitored by the company).
landing exit hi speed taxiway it's 60kt not to exceed 30kt upon reaching rwy exit.

i understand the next revision to the airbus auto-brake system will incorporate desired exit taxiway thru the FMGS.

Dakotablue
3rd Feb 2010, 15:26
i understand the next revision to the airbus auto-brake system will incorporate desired exit taxiway thru the FMGS.

I believe the A380 already has that. It's called 'Brake To Vacate' (BTV). Airbus is looking to make it standard equipment on their aircraft in the near future.

lalbak
3rd Feb 2010, 23:07
As for questions 1 and 2 (experience based on Fokker 50, CAT B):

I wouldn't really go any faster that 10 kts (dry runway) taking a 90 degree turn off the runway, it gets quite uncomfortable quickly (don't want to slam pax into the walls of the cabin). On determining the exist speed, for me, far and foremost the runway and taxiway conditions are most important. Take care when on contaminated runways and taxiways and extra care when in cold weather conditions. Besides that taxiway width, markings and visibility and aircraft CG position.

If the RET is designed for a 30 kt turnoff I'd do it at 30 kts depending, again, on conditions, taking care on heavily contaminated runways/taxiways.

Keep in mind that the Fokker 50 is an aircraft which will very easily slide on its nosewheel, like an "understeer" condition in a car.

NotaLOT
4th Feb 2010, 16:59
Thanks for all the replies, I welcome any other info, as I said, particularly from Code C aircraft pilots.

Northbeach
4th Feb 2010, 18:17
NotaLot,

I hope you find the following NG pilot’s perspective on your questions useful.

1) At what speed can you feasibly turn off into a 90 degree exit? What parameters of the exit impact on the exit speed, the width, the length, markings, knowledge of the airfield, visibility?

90 degree exists are the most uncomfortable for the passengers as there is the most side loading during the turn. My first concern is the condition of the surface, is it dry with excellent traction or is it covered with ice and frosted over with freezing rain? The better the traction the higher the speed I am comfortable with. With Mu readings of >40 then I can take the turn at 5 knots (guess as I am not usually looking at GPS speed readout while I am making a 90 degree turn), anything faster and it will be noticed and unpleasant for the passengers. The slower the better for 90 degree turns. All of the factors you mentioned are important; if I had to rank them then I would list them as:

A. surface condition-stopping ability
B. knowledge of the airfield
C. visibility, daylight
D. width
E. length: the longer the taxiway the higher the entry speed possible.
F. markings

My rankings are purely subjective.

2) If a runway has a RET that is designed to handle aircraft at speeds up to 30 knots, will you actually endeavor to use it at that speed? What factors affect your exit speed on a RET?

After operational safety my considerations are for passenger comfort. Usually I don’t make the first usable exit a priority. On a 1830 meter runway with braking reports of <40 Mu we use max autobrake and max thrust reverse so we are not adverse to heavy braking when necessary. The most important single factor affecting my exit speed is runway/taxiway surface condition, steering and stopping ability. This will vary from hour to hour, day to day and season for the same taxiway.

3) And this is particularly for A320/B737 pilots, how likely are you to be able to use a 30 knot RET located at 1500m from the threshold. I understand this is a very vague question, since there are so many factors that affect your braking performance, but some kind of general feeling on the matter would be very much appreciated, perhaps based on your experience at airports you fly to.

This has probably been answered, from this pilot’s perspective flying the NG full of people I try to make the experience as comfortable as possible for them. My landing, stopping, runway turn off and taxi plan is based on what “feels” comfortable based on now nearly 30 years in the industry. Though I am fairly comfortable with performance tables, engineering data and empirical analysis of mass in motion and brake energy requirements I do not approach my landing with the stated goal of making the 30 knot RET located at 1500m – unless I have to, and sometimes I do.Respectfully,

Northbeach

NotaLOT
4th Feb 2010, 19:16
Northbeach,

Thank you very much, this is exactly the kind of information I was hoping for, a pilot's perspective. I understand the NG is particularly demanding in terms of runway length for landing.

Is it usual for ATC to ask you to take a certain exit off a runway? Again I presume this very much depends on the airfield in question and presence of following traffic.

Intruder
5th Feb 2010, 03:15
747: 60 KIAS for a designated "high-speed" taxi exit; 10 KIAS for a 90 deg turn.

lynn789
5th Feb 2010, 03:32
I remember a 737 incident in australia where the pilots didnt realise they had asymetrical thrust, and in trying to correct with steering, the nosewheel slid sideways as the plane left the runway

the summing up stressed that too much shouldnt be asked or expected from the nosewheel or its tyre