The over use of autobrakes
Over many years as a 737 simulator instructor I have watched the almost robot like use of autobrakes for practically every landing regardless of the amount of excess runway length. One Asian operator uses Auto-brake 2 for every landing - good or bad weather. Given an all flaps up landing on a marginal length dry runway, the pilot still used Autobrake 2 "because that is what the SOP said." Needless to say he over-ran the end of the runway at 60 knots despite full reverse. When these pilots were asked to use manual braking, it was jerky, uncoordinated and the aircraft continually swerved either side of the runway centreline because lack of practice at manual braking.
One major Australian airline operating a Boeing 747 over-ran a 10,000 ft runway following a botched touch down in heavy rain. Due to a combination of crew errors the autobrake was inadvertently disarmed without the crew being aware. From that experience, the operator mandated that autobrakes were to be armed for every landing on its 737 fleet, regardless that the incident aircraft was a Boeing 747.
Many years ago a DC9 brake manufacturer published an article called "The High Cost of Heavy Braking" in which it compared the cost of tyre and brake wear when brakes were applied immediately on touchdown and at various lower speeds, with and without reverse thrust. The results demonstrated that instant brake application on touch down was by far the most expensive in terms of servicing costs.
It is instructive therefore to read the following comments made during a Boeing 727 flight operation symposium conducted in Seattle over 40 years ago by the Boeing Flight Operations Group.
Under the heading: Autobrakes - Wear and Usage, a question was asked "Did Boeing or operators register increased wear of wheels and brakes upon using the Autobrake System"?
Boeing replied:
"When we started using the Autobrake System, we made a 3-month evaluation within a group of thoroughly briefed check captains 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 that the correct use and application of Autobrakes and reverser needed emphasis.
The presentation [at this Symposium] 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 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 the touchdown point, autobrakes need not be used".
From the above comments it would seem that operators using the Autobrake System for all landings, regardless of perceived operational necessity, are wasting their money; as well as denying crews the opportunity to maintain manual braking skills.