NTSB: Ban Airlines From Reverser Use In Calculating Distances
Due in part to the recent fatal crash of a Southwest Airlines plane at Chicago, Midway Airport, in a press release issued January 27, 2006, the National Transportation Safety Board (NTSB) has urged the Federal Aviation Administration (FAA) to prohibit
airlines from using credit for the use of thrust reversers
when calculating stopping distances on contaminated runways.
The urgent safety recommendation is the result of
information learned by the NTSB during its investigation
into a fatal runway overrun in Chicago last month.
"We believe this recommendation needs the immediate
attention of the FAA since we will be experiencing winter
weather conditions in many areas of our nation for several
more months to come," NTSB Acting Chairman Mark V. Rosenker
On December 8, 2005, Southwest Airlines flight 1248, a
Boeing 737-7H4, landed on runway 31C at Chicago Midway
Airport during a snow storm. The aircraft failed to stop on
the runway, rolling through a blast fence and perimeter
fence and coming to rest on a roadway after striking two
vehicles. A 6-year-old boy in one of the automobiles was
While approaching Chicago on a flight from Baltimore,
the pilots used an on-board laptop performance computer
(OPC) to calculate expected landing performance.
Information entered into the computer included expected
landing runway, wind speed and direction, airplane gross
weight at touchdown, and reported runway braking action.
The OPC then calculated the stopping margin. Depending on
whether WET-FAIR or WET-POOR conditions were input, the
computer calculated remaining runway after stopping at
either 560 feet or 30 feet.
Both calculations were based on taking a stopping
credit assuming engine thrust reverser deployment at
touchdown. Flight data recorder information revealed that
the thrust reversers were not deployed until 18 seconds
after touchdown, at which point there was only about 1,000
feet of usable runway remaining.
The FAA does not allow the use of the reverse thrust
credit when determining dispatch landing distances; in fact,
historically decreases in stopping distances due to thrust
reverser deployment were used to offset other variables that
could significantly degrade stopping performance. However,
the FAA does permit thrust reverser credit for calculating
en-route operational landing distances for some transport
category aircraft, like the 737-700 series, but not for
others, like the 737-300.
If the thrust reverser credit had not been allowed in
calculating the stopping distance for flight 1248, the OPC
would have indicated that a safe landing on runway 31C was
not possible. "As a result," the Board said in its
recommendation letter, "a single event, the delayed
deployment of the thrust reversers, can lead to an unsafe
condition, as it did in this accident."
Although the recommendation would prohibit the thrust
reverser credit on all runways, its practical effect would
be felt on planned landings only on contaminated runways,
which is when the credit is included in stopping distance
Therefore, the Board is recommending that the FAA:
Immediately prohibit all 14 Code of Federal
Regulations Part 121 operators from using the reverse thrust
credit in landing performance calculations. (A-06-16)
(Urgent - this is the status indicated by the NTSB)