Following a public hearing the NTSB announced on Sep 13th 2016:
The NTSB investigation found that the probable cause of the accident – in which 29 of 127 passengers suffered minor injuries – was the captain’s inability to maintain directional control of the Boeing MD-88 due to his application of excessive reverse thrust, which degraded the effectiveness of the rudder in controlling the airplane heading. The aircraft was substantially damaged.
NTSB Chairman Christoper Hart said: “The passengers and crew of Delta flight 1086 were fortunate to have survived this crash with no loss of life or serious injuries.”
The NTSB identified following safety issues as result of the investigation:
– Use of excessive engine reverse thrust and rudder blanking on MD-80 series airplanes. The NTSB’s evaluation of flight data from Delta MD-88 airplanes showed that, despite company training and procedures on EPR targets, more than one-third of the landings captured by the data involved an EPR value of 1.6 or above, indicating the need for strategies to preclude excessive EPR use that could lead to rudder blanking. Such strategies, which could benefit all pilots of MD-80 series airplanes, include (1) identifying industry-wide best practices that have been shown to be effective in reliably preventing EPR exceedances during actual high-workload and high-stress operating conditions, (2) implementing a procedure in which the pilot monitoring would make a callout whenever reverse thrust power exceeded an operator’s EPR settings, and (3) exploring the possibility that an automated alert could help flight crews avoid EPR exceedances.
– Subjective nature of braking action reports. Even though the flight crew received two reports indicating that the braking action conditions on the runway were good, postaccident simulations showed that the braking action at the time that the accident airplane touched down was consistent with medium (or better) braking action. The flight crew’s landing performance calculations indicated that the airplane could not meet the requirements for landing with braking action that was less than good, but the flight crew proceeded with the landing based on, among other things, the reports indicating good braking action on the runway.
As part of its investigation of the 2005 Southwest flight 1248 accident at Chicago Midway International Airport, the NTSB issued safety recommendations to the Federal Aviation Administration (FAA) that addressed runway surface condition assessment issues, including the inherently subjective nature of pilot braking action reports. One recommendation—to outfit transport-category airplanes with equipment that routinely calculates, records, and conveys the airplane braking ability required and/or available to slow or stop the airplane during the landing roll and develop related operational procedures—has not yet been implemented because these systems are still under development and evaluation. The NTSB continues to encourage the FAA to develop the technology for these systems because they are expected to provide objective, reliable, real-time information that flight crews of arriving airplanes could use to understand the extent of runway surface contamination.
– Lack of procedures for crew communications during an emergency or a non-normal event without operative communication systems. Damage to the airplane during the accident sequence resulted in the loss of the interphone and public address system as methods of communication after the accident. As a result, the flight attendants in the aft cabin left their assigned emergency exits to obtain information from the flight crew and the lead flight attendant in the forward cabin. Also, the lead flight attendant left her assigned emergency exit to check on a passenger in the mid-cabin. However, because the airplane was not at a normal gate location or a normal attitude, an emergency evacuation was possible, but the flight attendants were not in a position to immediately open their assigned exits if necessary. Delta’s flight attendant manual and training curriculum did not address communicating during an emergency or a non-normal situation without operative communication systems. In addition, Delta did not have guidance instructing flight attendants to remain at their assigned exits during such a situation.
– Inadequate flight and cabin crew communication, coordination, and decision-making regarding evacuations for an emergency or a non-normal event. Postaccident interviews with the flight attendants indicated that the captain did not convey a sense of urgency to evacuate the cabin. The first officer stated, during a postaccident interview, that emergency response personnel requested, and the captain subsequently commanded, the evacuation. Postaccident videos provided by a passenger showed that the lead flight attendant announced the plans to evacuate about 6 minutes after the airplane came to a stop. The videos also showed that the flight attendants were confused about the timing of the evacuation, which did not begin until about 6 minutes after the evacuation announcement. In addition, the videos showed that more than 17 minutes had elapsed between the time that the airplane came to a stop and the time that all of the passengers were off the airplane.
10 safety recommendations have been released as result of the investigation.
The final report is going to be released.
The Aviation Herald
