Friday, August 22, 2008

Crash of Spanair MD-82 Could Have Been Prevented

One hundred fifty-three people were killed when a fully-loaded Spanair MD-82 crashed on takeoff from the Madrid airport on August 20, 2008. Witnesses describe an explosion in the left engine and the aircraft falling to the runway, veering off and then exploding into an inferno.

About one hour before the crash, the crew was reported to have aborted a takeoff because of a high temperature warning, known as an overtemp, from the left engine. Troubleshooting took place and the aircraft was again dispatched for a three-hour flight to the Canary Islands. The aircraft was full of fuel and the outside temperature was a warm 86 degrees Fahrenheit.

It is inexplicable and horrendous that an aircraft such as this was cleared for service without an engine change when they couldn’t possibly have known what damage resulted from the overtemp. This situation in a jet engine is a serious matter requiring extensive investigation, not merely an hour’s worth of troubleshooting. It does not happen without good, and usually serious, cause including imminent failure of hot section components, failure of compressor and fan assemblies or likely turbine disintegration.

Jet engines nearly always telegraph their imminent failure and this one surely did. It was ignored. The Pratt and Whitney JT8D engine has had a long and satisfactory service history starting with the Boeing 727, 737, DC-9 and all the MD-80's. While generally reliable, it has exploded all too frequently and is the subject of numerous service bulletins and airworthiness directives by the Federal Aviation Administration as well as aviation safety agencies in other countries. Some have exploded so violently that the containment rings that are designed to prevent penetration of debris into other critical aircraft components have proved to be insufficient.

When the MD-82 was built and certified, it was supposed to be able to safely fly with one engine if the other failed after reaching V1 (the speed at which it becomes safe to continue the takeoff in spite of the failure of an engine). However, the claim was substantiated by test pilots who know the engine will be simulated to fail, and not by flight crews who are totally surprised by the event on a hot day while fully loaded.

It is not surprising that the airplane didn't fly because expecting humans to perform to perfection is unreasonable, and the temperature and weight were likely well beyond the test parameters. At the controls were Spanair test pilots who were also victims of a cascade of events that came together to create this tragedy.

At this stage of aviation history, there is no reason for this disaster and both the horror and pain it has caused to so many families. Airline travel can and ought to be 100 percent safe if people do their jobs. This was an unnecessary accident.

Arthur Alan Wolk
August 22, 2008

Friday, August 1, 2008

Hawker 800 Crash In Minnesota–Some Preliminary Thoughts for All Pilots

A Hawker 800 executive jet aircraft crashed at a small airport in Minnesota, south of the Twin Cities on July 31, 2008. Witnesses describe a touchdown on a wet runway, a roll-out, then the application of power and a crash just beyond the end of the runway. All aboard were killed, either from impact or the ensuing fire.

The crew had successfully diverted around heavy weather and was landing in an area of moderate rain showers. Just before the crash, a wind shear alert was given (a rapid change in wind direction and velocity). Normally, a flight crew will add as much as 10 knots to the landing reference speed in the event of wind shear. The aircraft made it to the airport and the runway, and presumably the lift dump system was deployed, which should have allowed the aircraft to stop in 4,000 feet on a dry runway, according to the flight manual. It is typical for jet aircraft to touch down in the first 1,000 feet but, due to the wind shear, the first 1,500 feet may have been used. Therefore, except for the wet runway, 5,500 feet should have been sufficient for landing to a full stop, leaving about 750 to 1,000 feet remaining, if all went as expected. However, because of reported tail winds and standing water on the runway, it was questionable whether stopping in the available distance was possible. Hydroplaning, further increasing stopping distance, was also likely.

For all, or some of these reasons, the landing didn't go as expected. The crew elected to “go-around,” meaning they would have had to stow the left dump spoilers and flaps, and trim and apply takeoff power. The engines, likely idle by this time, would have had to spool up and the aircraft would have needed to accelerate again to take-off speed. The time to make the decision to go-around, stow the lift dump and achieve take-off thrust could have taken 10 to 15 seconds and used up another 1,000 to 1,500 feet of runway. That left precious little, or no, runway for the aircraft to accelerate to lift-off speed.

The aircraft did not leave the ground. Wheel tracks show that it left the pavement, traveled in the runway safety area–still on the ground–struck an antenna array, and then fell into a culvert where it burned. While there is no doubt the crew tried to save the aircraft, the decision to go-around on that size runway may have doomed the flight.

Investigators will review the cockpit voice recorder and, if equipped, the flight data recorder for clues and will look at the wreckage to determine the aircraft configuration at time of impact.

This information should confirm that unless there was a mechanical malfunction, this accident was preventable, like so many others of a similar type.
  • First, a go-around from idle thrust and with lift dump deployed on a 5,500 foot runway with this aircraft is nearly impossible under normal circumstances.
  • Secondly, aircraft performance charts are prepared to sell airplanes and bear little resemblance to actual performance achieved by average pilots in the field.
  • Thirdly, a pilot must always plan for contingencies and on this approach there was wind shear, lightning in the distance in all quadrants, heavy weather nearby and a short wet runway.

Even the best flight crew can find itself without options under circumstances like these. The tragedy of this accident reminds us all that aviation safety means no accident, whether it’s a mechanical malfunction, the combination of foul weather and a short runway, a faulty decision to go-around based upon inadequate aircraft performance information or just a mistake.

No conclusions can or should be drawn about this accident as the investigation has just begun, but these are some thoughts that bear consideration regardless of the ultimate findings.

Arthur Alan Wolk
August 1, 2008