A37575
17th Jul 2012, 12:27
It is fair to say that use of autobrakes for landing is now standard operaing procedure in many airlines; even though operationally they may not be required on the day. Wear and tear on tyres and brakes increase with autobrake use because the brakes are applied immediately on touch-down and therefore high energy absorbtion takes places. Use of full reverse allows the autobrakes to back off to maintain a selected deceleration rate but it is the initial high touch-down speed application where the wear occurs.
On that note, it is instructive to go back in time when autobrakes were relatively new to transport aircraft and read extracts from a Boeing 727 Flight Operations Symposium held at Boeing Seattle circa 1972. At the Symposium, Boeing received numerous complaints from 727 operators complaining of the extra costs involved with use of autobrakes. In reply to these criticisms, Boeing wrote (in part):
Question by Operators. "Did Boeing or operators register increased wear of wheels and brakes upon using the Autobrake System?"
Boeing reply: "When we started using the Autobrake System, we made a 3-month evaluation within a group of thoroughly briefed check cptains with no complaints. After general implementation we registered a sudden increase in the rate of replacements on wheels and brakes.
It was determined that much of the increase was attributable to improper use and techniques and the correct use and application of Autobrakes and reverser needed amplification.
The presentation on Autobrakes usage outlines Boeing's philosophy on when and how the autobrakes should be used. To re-emphasize; the autobrakes should be used on all landings when stopping distances are marginal. This is for short, wet or slippery runway conditions. Additionally, autobrakes should be used when the workload is higher than normal, such as engine out, low visibility, etc. This philosophy would suggest, during normal landing on long dry runways with the desired turnoff point a considerable distance from touchdown point, autobrakes need not be used.
Judicious use of brakes should be used on long dry runways with turnoff point far down the runway, to enhance brake and tire wear as well as promoting smooth comfortable deceleration for the passengers." Unquote.
It is instructive to see how the original Boeing philosophy on autobrake usage seems to have been long forgotten, with many operators directing that autobrakes should be used for all landings regardless of runway length.
As a postscript, this writer observed a crew in the simulator tasked with conducting an all-flaps up approach and landing to a marginal length dry runway. The company SOP for this type (Boeing 737 Classic) was to select Autobrake 2 for every landing regardless of runway length. Despite the obvious marginal length available for an all flaps up landing, the captain faithfully followed company SOP and selected autobrake 2.
With 185 knots Vref, the captain touched down close to the 1000 ft marker and applied full reverse . Soon after, and with the end of the runway coming up at high speed, he failed to over-ride the autobrakes and still in full reverse over-ran at 60 knots. Embarrassed and suffering loss of face, he then announced that the runway was too short for an all flaps up landing. His equally impassive first officer said nothing and stared straight ahead.
Perhaps there is a lesson here for readers. Blind use of autobrakes for every landing often results in lack of currency in manual braking techniques. This is noticeable in the simulator. Common-sense airmanship is eroded as complacency sets in. Operations management take note.:ok:
On that note, it is instructive to go back in time when autobrakes were relatively new to transport aircraft and read extracts from a Boeing 727 Flight Operations Symposium held at Boeing Seattle circa 1972. At the Symposium, Boeing received numerous complaints from 727 operators complaining of the extra costs involved with use of autobrakes. In reply to these criticisms, Boeing wrote (in part):
Question by Operators. "Did Boeing or operators register increased wear of wheels and brakes upon using the Autobrake System?"
Boeing reply: "When we started using the Autobrake System, we made a 3-month evaluation within a group of thoroughly briefed check cptains with no complaints. After general implementation we registered a sudden increase in the rate of replacements on wheels and brakes.
It was determined that much of the increase was attributable to improper use and techniques and the correct use and application of Autobrakes and reverser needed amplification.
The presentation on Autobrakes usage outlines Boeing's philosophy on when and how the autobrakes should be used. To re-emphasize; the autobrakes should be used on all landings when stopping distances are marginal. This is for short, wet or slippery runway conditions. Additionally, autobrakes should be used when the workload is higher than normal, such as engine out, low visibility, etc. This philosophy would suggest, during normal landing on long dry runways with the desired turnoff point a considerable distance from touchdown point, autobrakes need not be used.
Judicious use of brakes should be used on long dry runways with turnoff point far down the runway, to enhance brake and tire wear as well as promoting smooth comfortable deceleration for the passengers." Unquote.
It is instructive to see how the original Boeing philosophy on autobrake usage seems to have been long forgotten, with many operators directing that autobrakes should be used for all landings regardless of runway length.
As a postscript, this writer observed a crew in the simulator tasked with conducting an all-flaps up approach and landing to a marginal length dry runway. The company SOP for this type (Boeing 737 Classic) was to select Autobrake 2 for every landing regardless of runway length. Despite the obvious marginal length available for an all flaps up landing, the captain faithfully followed company SOP and selected autobrake 2.
With 185 knots Vref, the captain touched down close to the 1000 ft marker and applied full reverse . Soon after, and with the end of the runway coming up at high speed, he failed to over-ride the autobrakes and still in full reverse over-ran at 60 knots. Embarrassed and suffering loss of face, he then announced that the runway was too short for an all flaps up landing. His equally impassive first officer said nothing and stared straight ahead.
Perhaps there is a lesson here for readers. Blind use of autobrakes for every landing often results in lack of currency in manual braking techniques. This is noticeable in the simulator. Common-sense airmanship is eroded as complacency sets in. Operations management take note.:ok: