Wading through the rampant rumors following last week's tragic
snowstorm-related Southwest Airlines accident at Chicago's Midway
airport, a number of factors, involving thrust reversers or braking
action, are starting to be seen as possible causes or causal
factors in the investigation.
Southwest Airlines' Flight 1248 was involved in the accident at
Chicago Midway Airport at approximately 7:15 p.m. CST while the
aircraft, a Boeing 737-700, was landing. The aircraft veered off
the runway onto Central and 55th Avenue, beyond the northwest
corner of the runway. Flight 1248 was scheduled for a 2:55 p.m. CST
departure out of Baltimore/Washington International Airport, but
the aircraft's departure was delayed until 4:50 p.m. CST because of
weather. The flight arrived at Chicago Midway at 7:15 p.m., after
circling the Chicago Midway Airport for approximately 35
minutes.
Weather reports indicate that the aircraft was dealing with as
low as a 200 foot ceiling and visibility estimated at anywhere from
1/4 to 3/4 mile. The passenger list indicated the aircraft carried
98 passengers with a crew of five.
The aircraft involved was a Boeing 737-700, N471WN (although
official SWA statements originally named it as 'tail number
N-471'). Southwest took delivery of this new aircraft in July 2004.
The 737-700 has the same fuselage as the 737-300 and is fitted with
a new generation of wings, stabilizers, and tail sections. The
737-700 is 110 ft 4 in long and can carry up to 148 passengers in
an all-economy configuration. The aircraft was released from the
airline's Phoenix maintenance facility on Dec. 7, 2005. There were
no indications that the aircraft was experiencing any type of
maintenance problems.
The Southwest Airlines Captain on Flight 1248 has been flying
for the airline for ten years. The Southwest Airlines First Officer
on Flight 1248 has been flying for the airline for more than two
years.
NTSB sources, quoted in the general media, are starting to talk
about a lack of deceleration after touchdown on Midway's 6500 foot
runway that indicates a number of possibilities... or a combination
thereof. Among items in question are how much of the runway was
used in the initial touchdown, when the Boeing's two thrust
reversers were actuated, when they actually deployed and what
effect braking action played in the matter. Initial concerns about
excessive approach and touchdown speeds (the culprit in SWA's one
other serious accident in Burbank, CA) appear to have been
down-played by NTSB personnel since the pilots were interviewed on
Saturday and as the CVR and FDRs were examined in Washington.
Robert Benzon, National Transportation Safety Board investigator
in charge, said that, "They all said it was a smooth landing but
they could sense a lack of deceleration."
Media reports suggest that both pilots have indicted that the
aircraft did not immediately respond to a command to actuate thrust
reversers as the aircraft attempted to decelerate on airport that
had seen 7-9 inches of snow that day.
Keith Holloway, a spokesman for the National Transportation
Safety Board, added that, "The captain told us when he initially
tried the thrust reversers, he couldn't do it."
Southwest CEO, Gary Kelly, has also confirmed that the flight
crew selected to deactivate the auto-braking system in order to
give them more direct control over the situation... a move defended
by Kelly in statements to the media, "We let our flight crews make
the determination to brake the aircraft. It's just a choice, and we
think that it's been obviously very, very successful over a long
period of time."
Boeing corroborated the fact that auto-braking selection is a
choice left to flight crews and that Boeing does not mandate its
use for such operations... nor do they see anything unusual in
leaving such a decision to the cockpit crew. Boeing spokesperson
Liz Verdier explained that, "There is not a right or a wrong way to
do that... They are used or not used in accordance with conditions
or airline operational procedures."
One associated news item that is making the rounds, concerns
older airports and short runways, and is no secret to the world of
aviation as regards some of the elder airports that make up
the nation's air transport network. Midway was built in 1923 and
quickly surrounded by houses and businesses that were unrestricted
in building up around and close to the airport. It is one of some
300 US commercial airports without 1,000-foot buffer zones
bordering their runways. The end of the runway used by SWA 1248 was
reportedly only 280 feet from the perimeter fencing of the
airport.
A number of programs have been developed to try and mitigate
some of these issues, including one that has proven to be quite
successful and cost-effective. The use of beds of 'crushable
concrete' slow aircraft as the progress off a runway and toward the
perimeter... the effect is quite striking in that is not only
decelerates the aircraft aggressively but does so in a fashion that
minimizes the possibility of passenger injury and, to an extent,
aircraft damage. This program, known as Engineered Material
Arresting Systems, are currently in use at 18 runways at 14
airports, where they have already been employed to arrest
accidental overruns on three occasions since their first use in May
1999 at NYC's Kennedy Airport.