Southwest Airlines Flight 1248

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Southwest Airlines Flight 1248
Southwest Airlines Flight 1248 -1.jpg

The damaged Boeing 737 behind the runway
Accident summary
Accident type Rolling over the runway
place Chicago Midway Airport
date December 8, 2005
Fatalities 1 (on the ground)
Survivors 103 (all on the plane)
Injured 14 (3 on the floor)
Aircraft
Aircraft type Boeing 737-7H4
operator Southwest Airlines
Mark N471WN
Passengers 98
crew 5
Lists of aviation accidents

Southwest Airlines flight 1248 was a flight of the American airline Southwest Airlines with a Boeing 737-7H4 , which came on December 8, 2005 from Baltimore when landing at Chicago-Midway Airport over the end of the runway and came to a stand on a street came. There, the machine buried a car under it, with a six-year-old boy, Joshua Woods, dying, the other four family members were slightly to partially seriously injured.

procedure

On Thursday, December 8, 2005, the machine, a Boeing 737-700 of Southwest Airlines, took off from Baltimore for Chicago . Due to heavy snowfall at the destination airport, the start was two hours late.

The weather information communicated to the cockpit crew most recently reported tail winds of 8 knots for the planned runway 31C. The flight operations manual and the airline's guidelines allow landings at a maximum of 10 knots. If the braking effect is poor, such as B. can be the case with snow and ice, the maximum wind speed is reduced to 5 knots. Following this, the crew decided to fly to a replacement airport (Kansas City or St. Louis, Missouri) if bad conditions were reported for the entire runway. Calculations by the “ On Board Performance Computer ” erroneously showed that in such a case and with a 10 knot tail wind the aircraft would come to a standstill approx. 12 meters before the end of the runway.

At 19:12 local time (CST), air traffic control gave the machine clearance for runway 31C. The estimated braking effect was last reported as “ mediocre ” for the first half and “ poor ” for the second half of the runway, which was considered sufficient.

The machine touched down properly, leaving around 1,400 meters of the 1988 meter long track to brake. The crew used the automatic braking system at the maximum setting, but noticed an insufficient speed reduction a few seconds after landing and then braked manually. The first officer only activated reverse thrust 15 seconds after touching down, after realizing that this had not yet happened.

Due to the excessive speed, the Boeing overshot the runway, lost its nose landing gear, broke two fences, and finally reached a public road where it collided with a vehicle traveling north, before - at 7:14 p.m. - with its nose open the floor - came to a standstill.

Investigations

The National Transportation Safety Board (NTSB) began investigating immediately after the accident . The main cause of the accident was found to be the late activation of the reverse thrust, which led to a braking distance that was too long. Both pilots stated that they were distracted by the automatic braking system and therefore overlooked activating the reverse thrust in good time, which meant that it could only develop its full effect 18 seconds after landing. The pilots had no previous experience - not even in the simulator - with the new automatic braking system.

The NTSB blamed the airline on the following points:

  • Southwest Airlines had not given clear and coherent instructions and training on landing calculations. While the airline assumed that mixed information on the braking properties of a runway would be based on the worst, this was not consistently communicated to the employed pilots and was accordingly not followed. The NTSB found several cases in which other crews acted similarly to that of Southwest Airlines flight 1248 for the day of the accident.
  • The decision to land was disrupted by the inadequate design and programming of the “ On Board Performance Computer ” (OPC). This computer, an airline laptop, is used to calculate the possibility of a landing and the necessary braking distance and showed the crew of Flight 1248 a long enough runway for even the worst conditions, but this was incorrect:
  1. When entering a bad braking effect, tail winds over 5 knots were ignored, as this was the maximum permitted value according to guidelines. The user was not informed about this, however, the calculation with an input of 8 or 10 nodes always took place with 5 nodes, although the opposite was indicated. The NTSB assumes that the pilots would have made more cautious decisions if the calculations were correct.
  2. When calculating the braking distance, the OPC assumes that the thrust reverser is activated manually, which has a positive effect on braking performance. However, this was not known to the pilots of the accident machine, as the computer did not provide any information about this and the manuals were inadequate. In this case, too, the NTSB assumes that the crew would have opted for an alternative airport with the knowledge.
  • The introduction of a new automatic braking system without giving the pilots the opportunity to adjust to it in a transition phase and to practice under lighter weather conditions and longer runways was judged to be poor. This forced the crew to make their first landing with this system under the difficult conditions in Chicago, which distracted from the timely activation of the reverse thrust. Other pilots in the company also reported distractions during the first landings.

According to the NTSB, the pilots' decision not to fly to an alternate airport and to attempt a landing at Chicago Midway Airport with its very short runways despite critical conditions also contributed to the accident. The nearest airport is Chicago O'Hare International Airport , 20 miles away , which has much longer runways.

Ultimately, the NTSB classifies as decisive for the severity of the accident that although the airport has only a small safety distance to civil infrastructure, there was no Engineered Materials Arrestor System (EMAS) in place.

consequences

The NTSB recommended the following measures, among others:

  • Compulsory calculations before landing (and not just before departure, as was previously the case) with updated data on weather and runway condition with a sufficient safety factor of at least 15 percent.
  • In the future, the calculation will be based on the runway's worst braking effect, minus a safety factor of 15 percent.
  • Ensuring that all computers used carry out verifiable calculations and that users are informed about all important factors
  • Improved pilot training
  • Change of the landing procedure so that the non-flying pilot will in future check the state of the thrust reverser immediately after touchdown (if available)
  • The thrust reversal should no longer be taken into account when calculating the braking distance.

Today it is common before and after new runways so-called "Runway Safety Area" to German "runway safety zone" to keep free. This makes it less dangerous if an aircraft shoots over the runway.

The runways at Chicago Midway Airport have been equipped with EMAS since 2007, which are designed to brake aircraft rolling off the runway.

See also

swell

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