On March 8, 2017, about 1452 eastern standard time, Ameristar Air Cargo, Inc., dba Ameristar Charters, flight 9363, a Boeing MD-83 airplane, N786TW, overran the departure end of runway 23L at Willow Run Airport (YIP), Ypsilanti, Michigan, after the captain executed a rejected takeoff. The 110 passengers and 6 flight crewmembers evacuated the airplane via emergency escape slides; however, one slide failed to inflate and could not be used. One passenger received a minor injury, and the airplane sustained substantial damage. The airplane was operated under the provisions of Title 14 Code of Federal Regulations (CFR) Part 121 as an on-demand charter flight and was destined for Washington Dulles International Airport, Dulles, Virginia. Visual flight rules conditions prevailed at YIP at the time of the accident.
During the takeoff roll, the captain, who was the pilot flying, executed the rejected takeoff 12 seconds after the airplane achieved V1 (takeoff decision speed) because he perceived that the airplane did not respond normally when he pulled back on the control column to command rotation. (V1 is defined, in part, as the maximum speed in the takeoff by which a rejected takeoff must be initiated to ensure that a safe stop can be completed within the remaining runway.) The check airman, who was the pilot monitoring (and was providing airplane differences training to the captain), questioned the captain’s decision to reject the takeoff after V1 but adhered to company standard operating procedures and did not attempt to intervene.
Data from the airplane’s flight data recorder (FDR) showed that the airplane’s right elevator was positioned full trailing edge down (TED) when the flight crew first powered up the airplane on the day of the accident and remained there throughout the accident sequence. An airplane performance study (based, in part, on FDR data) confirmed that the airplane did not respond in pitch when the captain pulled on the control column. Based on the study’s comparison with a previous takeoff, the National Transportation Safety Board (NTSB) determined that the airplane’s lack of rotational response to the control column input did not become apparent to the captain in time for him to have stopped the airplane on the runway.
Before the accident flight, the airplane had been parked on the ramp at YIP for 2 days near a large hangar, and the elevators (which, by design, did not have gust locks) were exposed to high, gusting surface wind conditions. Postaccident examination showed that the right elevator’s geared tab’s inboard actuating crank and links had moved beyond their normal range of travel and became locked overcenter, effectively jamming the right elevator in a full-TED position and rendering the airplane incapable of rotation during takeoff. The speed of the surface wind and gusts at YIP did not exceed the certification design limit or maintenance inspection criteria for the airplane. However, the NTSB determined the airflow at the airplane’s parked location was affected by the presence of the large hangar that generated localized turbulence with a vertical component that moved the elevator surfaces rapidly up and down, which resulted in impacts against the elevator mechanical stops, imposing dynamic loads sufficient to jam the right elevator.
As a result of this investigation, the NTSB identified the following safety issues:
Lack of a means to enable flight crews of Boeing DC-9/MD-80 series and 717 model airplanes to verify before takeoff that the elevators are not jammed. The accident flight crew performed both the preflight inspection and the control check during taxi in accordance with the procedures in Ameristar’s Aircraft Operating Manual (AOM) for the Boeing MD-83; however, these checks did not enable them to detect the jammed elevator condition. For all Boeing DC-9/MD-80 series and 717 model airplanes (which have a similar elevator design), a full-TED elevator position (which may be visible during the preflight walkaround inspection) is not necessarily indicative of an anomaly because the elevators can freely move to that position under a nominal ground wind. Also, on these airplane models, the control column is mechanically connected to and directly controls the elevator control tabs, not the elevators. During the taxi control check for the accident airplane, the elevator control tabs responded normally to control column input, even though the right elevator was jammed.
Need for lower ground gust criteria for elevator physical inspections and operational checks by maintenance personnel for Boeing DC-9/MD-80 series and 717 model airplanes. The AOM contained an amplified normal checklist for flight crews that included a caution that airplanes exposed to high sustained wind or gusts greater than 65 kts were susceptible to elevator damage and/or jamming and stated that, for any airplanes suspected of such exposure, inspections and checks specified in Ameristar’s Aircraft Maintenance Manual (AMM) for the Boeing MD-83 were required. The AMM included a warning that the airplane must be parked headed into the wind if gusts were expected to exceed 60 kts and a caution that visual and physical inspections of all flight control surfaces were required if the airplane was subjected to wind exceeding 65 kts. However, none of the recorded or forecasted wind at YIP exceeded these limits during the time that the airplane was parked on the ramp (the highest reported wind gust was 55 kts and the highest forecasted gust was 48 kts).
Potential inadequacy of ground gust limit loads for the certification of transport category airplanes. The airworthiness standard current at the time of the accident specified in 14 CFR 25.415, “Ground gust conditions,” that flight control systems and surfaces of transport-category airplanes must be designed for the limit loads generated when the airplane is subjected to a 65 kt horizontal ground gust from any direction while parked and taxiing. The regulation allowed for the assumption of static loads and provided the formula from which the hinge moments must be computed for elevators. However, considering the circumstances of the accident, the NTSB is concerned that the ground gust criteria specified in the regulation may not adequately ensure that critical flight control systems are protected from hazards introduced by ground gusts that contain dynamic, vertical wind components.
Lack of procedures for operators of Boeing DC-9/MD-80 series and 717 model airplanes to monitor the wind that affects parked airplanes. Although the AOM and AMMspecified actions for flight crews and maintenance personnel to take when ground gusts reached certain criteria, Ameristar had no procedures to identify who was responsible for monitoring the known and forecasted wind that may affect the company’s parked airplanes. Had the wind at YIP exceeded the ground gust criteria specified in the AOM and AMM, it is unclear from Ameristar’s procedures if any personnel would have known and subsequently ensured that the specified parking and/or inspection actions were taken. To ensure that the elevators of Boeing DC 9/MD 80 series and 717 model airplanes are inspected by maintenance personnel when exposed to ground gusts that meet or exceed criteria specified in the AMM, all operators of these airplanes must maintain awareness at all times of the forecasted and known wind where the airplanes are parked. After the accident, Ameristar implemented procedures for monitoring the wind affecting its parked airplanes.
Lack of procedures for weather observers related to sign off and backup augmentation responsibilities during a facility evacuation. YIP was a Limited Aviation Weather Reporting Station (LAWRS) facility, and, on the day of the accident, all personnel evacuated from the air traffic control tower due to the high wind. Further, due to a power outage, the automated surface observing system (ASOS) lost some of its sensor functions. Before evacuating the duty station, a LAWRS observer did not sign off from the ASOS operator interface device (OID), and, after evacuating, no LAWRS observer provided any backup information to supplement the weather data that was missing from the partially disabled ASOS. As a result, throughout the day of the accident, the ASOS continued to automatically disseminate aviation routine weather reports (METARs) that did not contain the AUTO modifier (because the observer did not sign off from the OID) to show that the METARs were not being augmented by a weather observer and did not contain complete weather information.1 The investigation identified procedural gaps in Federal Aviation Administration (FAA) Order JO 7900.5D (which was current at the time of the accident) and its subsequent revision in Change 1 (effective November 29, 2017) that could be clarified to ensure dissemination of the most complete and accurate weather information possible during circumstances in which weather observers are unable to perform their prescribed duties from their normal duty stations during normal duty hours.
Evacuation slide malfunction. The evacuation slide for the airplane’s right front (1R) door did not inflate when a flight attendant pulled the manual inflation handle, which rendered the exit unusable. The investigation found that the cable had been installed incorrectly in the valve assembly, which prevented proper inflation. On July 14, 2017, the slide manufacturer issued a revision to the Component Maintenance Manual to provide more descriptive valve testing procedures intended to prevent improper cable installation.
During the overrun, the airplane was traveling about 100 kts when it exited the paved surface off the departure end of runway 23L at YIP. It then traveled about 950 ft across the grassy part of the runway safety area (RSA) before striking the airport perimeter fence and a raised, paved road before coming to a stop. The RSA off the departure end of runway 23L met the dimensional standards specified in FAA Advisory Circular 150/5300-13A, Change 1, having been upgraded between 2006 and 2009. The NTSB notes that these upgrades were responsive to previously issued NTSB safety recommendations and were part of a national program that the FAA initiated in 1999 to improve RSAs, install engineered material arresting systems, and relocate or make frangible FAA-owned navigational aids located in an RSA.
The NTSB determines that the probable cause of this accident was the jammed condition of the airplane’s right elevator, which resulted from exposure to localized, dynamic wind while the airplane was parked and rendered the airplane unable to rotate during takeoff. Contributing to the accident were (1) the effect of a large structure on the gusting surface wind at the airplane’s parked location, which led to turbulent gust loads on the right elevator sufficient to jam it, even though the horizontal surface wind speed was below the certification design limit and maintenance inspection criteria for the airplane, and (2) the lack of a means to enable the flight crew to detect a jammed elevator during preflight checks for the Boeing MD-83 airplane. Contributing to the survivability of the accident was the captain’s timely and appropriate decision to reject the takeoff, the check airman’s disciplined adherence to standard operating procedures after the captain called for the rejected takeoff, and the dimensionally compliant runway safety area where the overrun occurred.
As a result of this investigation, the NTSB makes safety recommendations to the FAA and The Boeing Company and reclassifies two previously issued safety recommendations to the FAA.