surface conditions & stopping ability.
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