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MD88, New York La Guardia USA, 2015
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|On 5 March 2015 a Boeing MD88 veered off a snow-contaminated runway 13 at New York La Guardia soon after touchdown after the experienced flight crew applied excessive reverse thrust and thus compromised directional control due to rudder blanking, a known phenomenon affecting the aircraft type. The aircraft stopped partly outside the airport perimeter with the forward fuselage over water. In addition to identifying the main cause of the accident, the Investigation found that exposure to rudder blanking risks was still widespread. It also noted that the delayed evacuation was partly attributable to inadequate crew performance and related Company procedures.|
|Actual or Potential
|Human Factors, Runway Excursion, Weather|
|Flight Conditions||On Ground - Normal Visibility|
|Aircraft||MCDONNELL DOUGLAS MD-88|
|Operator||Delta Air Lines|
|Type of Flight||Public Transport (Passenger)|
|Intended Destination||LaGuardia Airport|
|Take off Commenced||Yes|
|Location - Airport|
|Tag(s)||Inadequate Aircraft Operator Procedures,|
Deficient Crew Knowledge-performance
|Tag(s)||Flight / Cabin Crew Co-operation,|
Inappropriate crew response - skills deficiency,
Plan Continuation Bias,
Procedural non compliance,
Landing Performance Assessment,
Off side of Runway,
Ineffective Use of Retardation Methods
|Damage or injury||Yes|
|Causal Factor Group(s)|
On 5 March 2015, a Boeing MD88 (N909DL) being operated by Delta Airlines on a scheduled passenger flight from Atlanta GA to New York La Guardia as DL1086 left the side of runway 13 at destination in normal day visibility soon after touchdown from an ILS approach. The aircraft partly penetrated the airport perimeter before stopping with the front of the aircraft over the water which lies just outside the runway retaining wall. The aircraft sustained "substantial damage" but only 29 of the 132 occupants sustained minor injuries.
An Investigation was carried out by the NTSB. The FDR, CVR and QAR were recovered and data from all three was successfully downloaded. The data recorded on the QAR was the same as that recorded on the FDR but "because of issues with data signal dropouts from the FDR magnetic tape, both FDR and QAR data were used”. It was found that "all parameters, except for those related to engine speed and pressure altitude, (had become) invalid during the accident landing" as a result of damage sustained by the aircraft prior to a loss of electrical power to the FDR and QAR.
It was noted by the Investigation that the both pilots were "highly experienced" in MD-88 operations. The 56 year-old Captain, who had been PF for the accident flight, had been a Delta employee since leaving the USAF in 1989. He had accumulated about 15,200 total flight hours which included about 11,000 hours on the MD88/MD90 and had about 9,700 hours in command. The 46 year-old First Officer had joined Delta on the Boeing 737 in 2007 after working as a Boeing 727 Flight Engineer since 2001 when he left the US Navy. He had accumulated about 11,000 total flight hours which included about 3,000 hours on the MD88/MD90 since qualifying on type in 2011.
It was established that the crew had been well aware of the likelihood that the runway conditions they could expect on arrival at La Guardia would be at least "challenging" and a landing might not be possible. Considerable discussion and performance data review occurred en route from Atlanta. Requests for braking reports about 45 and 35 minutes before the estimated landing time could not be met because the landing runway 13 was at that time closed for snow clearance and this was considered to have "created some situational stress for the Captain". Once the runway was reopened, two aircraft which landed about 16 and 8 minutes before the accident landing reported "good" braking action so the pilots "expected to see at least some of the runway’s surface" once clear of cloud on the ILS approach. Instead, what they saw as the Captain called "runway in sight" at about 230 feet agl was a runway covered with snow. They had already determined that they needed "good" braking action to be able to land and that anything less would require a diversion so that the "snowier-than-expected" runway plus its relatively short (2,135 metre) length and the presence of Flushing Bay directly off the departure end of the runway "most likely increased the Captain’s concerns" and "exacerbated his situational stress".
Main gear touchdown occurred with the aircraft aligned with and close to the centreline at 180 metres past the threshold. Almost immediately the Captain made an "aggressive" deployment of the thrust reversers. But almost as soon as the First Officer had called "two in reverse", and just 5 seconds after reverser deployment, he followed it with "out of reverse" and then "come out of reverse" and immediately repeated it. The Captain promptly responded - FDR data showed that the reversers were stowed within 2.5 seconds - but the aircraft had already begun to deviate left and it became apparent that directional control could not be achieved by right rudder input or differential braking and the aircraft left the side of the runway at a distance of 975 metres from the runway threshold. As the excursion progressed (see the diagram below) the First Officer shut down both engines "to prevent any further thrust from pushing the airplane into Flushing Bay" and the Captain subsequently stated that the nose of the aircraft had broken through a fence on the perimeter sea wall and that "both he and the First Officer could see the water below" as the aircraft came to a stop.
It was found that electrical power was no longer available (the aircraft batteries had been damaged during the excursion) which precluded normal crew communications. At some point, the captain went into the passenger cabin and asked the senior cabin crew to "assess the exits". After a few minutes, the First Officer used his cell phone to call company dispatch, which transferred the call to the La Guardia TWR and he advised the final head count (taken from the pre-take-off ACARS Report which did not include two infants) and the fuel quantity. The flight crew completed "those parts of the evacuation checklist that could be done without power" and according to the First Officer, a firefighter approached the window on (his) side of the flight deck and told him through a partially opened window that "everyone should evacuate the airplane via the right overwing exits due to fuel leaking from the left wing". The First Officer advised the Captain accordingly and the latter then told the cabin crew to "begin evacuating the passengers from the right overwing exits and the tailcone exit".
ATC were initially not aware of the excursion due to the poor visibility from the TWR and reports from airport personnel nearer to the scene lacked an adequate description of the aircraft location but did promptly communicate to ATC to the effect that the runway was "closed". Emergency vehicles did not leave their station until 4 minutes after the aircraft had stopped and did not reach the aircraft for a further 4 minutes. It was concluded from available timed video evidence that the evacuation had not begun until about 12 minutes after the aircraft had come to a stop (and about 6 minutes after passengers were first told that an evacuation would be necessary) and that a further 5 minutes elapsed before the last of the passengers had left the aircraft. Prior to the commencement of the evacuation, there was considerable evidence of both confusion amongst the cabin crew and lack of assertiveness on the part of the flight crew. It was concluded that "given that the airplane was stopped off the runway at an unusual attitude and with damage, the Captain’s decision to evacuate the airplane should have come earlier in the sequence of events and before the request from ARFF personnel to evacuate".
The use of reverse thrust was closely examined using FDR data. It was found that although both pilots were aware that the "target" Engine Pressure Ratio (EPR) for reverse when landing on a contaminated runway was 1.3, EPR values were found to have exceeded 1.6 for about 5 seconds whilst the airspeed was under 130 knots, the left engine reaching a maximum of 2.07 and the right engine reaching a maximum of 1.91. Boeing data showed that, "with reverse thrust above 1.6 EPR and an airspeed under 146 knots, the rudder had limited directional authority" so that during the 4.5 seconds between the beginning of deviation from the runway centreline and time that the thrust reversers were stowed, the rudder had been "blanked" by the effect of the thrust reversers so that rudder input was unable to control heading. Once the thrust reversers were stowed and rudder authority was restored, it had been possible to reduce the extent of the displacement.
The possible causes of the initial deviation to the left - the slightly asymmetric application of reverse thrust, a suddenly increased crosswind component and the application of braking during the landing roll - were examined and it was concluded that it was unlikely that any single event or environmental factor would have been able to create the effect which prevailed on its own and that a combination of these factors probably favoured the initiation of a deviation.
The Investigation compared FDR data from the previous landing aircraft, also Delta MD88, and that although the first aircraft had also recorded a significant exceedance of the "target" 1.3 EPR (reaching 1.82 and 1.53), it had remained on the runway centreline throughout its landing roll. Simulations using the two sets of wheel braking coefficients showed that both indicated "medium" braking action had prevailed and it was therefore concluded that "although the runway was contaminated with snow, runway friction when the accident airplane landed was sufficient for stopping on the available runway length". It was noted that contrary to Delta guidance to MD-88 pilots to "consider delaying thrust reverser deployment until nosewheel touchdown so that directional control would not be affected by asymmetric deployment", the accident aircraft Captain had "deployed the thrust reversers almost simultaneously with the main landing gear touchdown".
Landing flight data from 80 other Delta MD88 landings was examined and it was found that target EPR for both dry runways (1.6) and contaminated runways (1.3) were regularly exceeded. Over half of those on non-dry runways had maximum EPRs for both engines above 1.3 (although none went as high as those on the accident aircraft) and nearly half of all the reviewed landings recorded at least one engine maximum EPR in excess of 1.6. Also, it was found that in none of the other landings in which at least one engine registered above 1.6 EPR had the reverse thrust been applied as rapidly as was the case with the landing under investigation.
A total of 14 previous events in the USA over the 20 year period 1995 -2015 involving loss of directional control during landing by MD-80 series aircraft were also examined. All but one had occurred on a contaminated runway and a clear majority had involved use of reverse thrust which exceeded 1.3 EPR.
The formally documented Conclusions of the Investigation included the following in respect of the causation and immediate aftermath of the accident:
- Uncertainty about the runway conditions at LaGuardia Airport led to some situational stress for the Captain.
- Although the runway was contaminated with snow, runway friction when the accident airplane landed was sufficient for stopping on the available runway length.
- The circumstances associated with the landing, including the snowier-than-expected runway, short runway length, and body of water off the departure end of the runway, likely exacerbated the captain’s situational stress and prompted him to make an aggressive input on the thrust reversers.
- The Captain was unable to maintain directional control of the airplane due to rudder blanking, which resulted from his application of excessive reverse thrust.
- Even though the First Officer promptly identified rudder blanking as a concern and the Captain stowed the thrust reversers in response, the airplane’s departure from the left side of the runway could not be avoided because directional control was regained too late to be effective.
- The flight and cabin crews did not conduct a timely or an effective evacuation because of the flight crew’s lack of assertiveness, prompt decision-making, and communication and the flight attendants’ failure to follow standard procedures once the Captain ordered the evacuation.
Other Conclusions related to prevention of a recurrence included the following:
- A solution to reliably limit reverse thrust engine pressure ratio values could benefit all pilots of MD-80 series airplanes.
- A callout when reverse thrust exceeds 1.3 engine pressure ratio during landings on contaminated runways could help avoid rudder blanking and a subsequent loss of directional control.
- An automated alert could help minimize the possibility of reverse thrust EPR exceedances during the landing rollout.
- This accident demonstrates the continuing need for objective, real-time, airplane-derived data about runway braking ability for flight crews preparing to land with runway surface conditions that are worse than bare and dry.
- By not using its continuous friction measuring equipment during winter operations, LaGuardia Airport did not take advantage of a tool that would allow the airport to objectively assess the effectiveness of snow removal operations on contaminated runways.
- The airport winter operations safety guidance provided by the FAA is not sufficiently clear about the timing and need for updated runway condition reports, which could result in flight crew uncertainty about possible runway contamination.
- This and other accidents demonstrate the need for improved decision-making and performance by flight and cabin crews when faced with an unplanned evacuation.
- The flight attendants were not adequately trained for an emergency or unusual event that involved a loss of communications after landing, and the flight attendants’ decision to leave their assigned exits unattended after the airplane came to a stop resulted in reduced readiness for an evacuation.
- Aircraft Rescue and Firefighting personnel would likely have arrived at the accident scene sooner if they had received more timely and precise information about the accident and its location.
The Investigation identified seven Safety Issues as a result of the Investigation:
- The use of excessive engine reverse thrust and rudder blanking on MD-80 series airplanes
- An 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 were capable of benefiting all pilots of MD-80 series airplanes.
- The 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, post-accident 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. It was noted that one of the Safety Recommendations made as a result of the Southwest Airlines Boeing 737 overrun accident at Chicago Midway in 2005 had been to equip transport-category aircraft with a system which could routinely calculate, record and convey to pilots the braking action required and/or available during the landing roll has not yet been implemented.
- The lack of procedures for crew communication during an emergency or a non-normal event without operative communication systems
- Damage to the aircraft during the accident sequence resulted in the loss of the interphone and public address system as methods of communication after the accident. Because the flight attendants then left their assigned emergency exits at a time when an emergency evacuation order might reasonably have been expected, they were not in a position to immediately open their assigned exits if necessary. Their training had not covered emergency communication without normal communication systems and there was no requirement for them to remain at their assigned exits during such a situation.
- Inadequate crew communication, coordination and decision-making regarding aircraft evacuation
- There had been a delay in evacuation due to the lack of a prompt order and the failure to communicate any sense of urgency when it was ordered with evacuation prompted only by RFFS personnel who had found evidence of a fuel leak. Despite many previous accident investigations which have found similar evacuation-related issues, "FAA efforts to fully address the issues have so far been insufficient".
- The inaccurate passenger counts provided to emergency responders
- Although it had no direct bearing on the aftermath of the investigated accident, the failure of the aircraft crew to provide an accurate head count to RFFS personnel upon exiting the aircraft was of concern and needed to be addressed.
- Unclear policies regarding runway friction measurements
- La Guardia and other airports operated by the Port Authority of New York and New Jersey were not using continuous friction measuring equipment (CFME) to assess runway friction after snow removal operations when relevant documentation stated that they would do so. As a result, the Port Authority’s policies regarding CFME use during winter operations need clarification, especially given that the FAA promotes CFME as a valuable tool for airport operators to detect trends in runway conditions during such operations.
- Unclear policies regarding runway condition reporting
- FAA guidance on airport winter safety and operations states that NOTAMs describing runway surface conditions must be “timely” and be updated any time a “change to the runway surface condition” occurs. At the time of the accident, the current NOTAM was 2 hours old and since then snowfall had continued and accident runway had been closed for snow clearance prior to reopening. Flight crew access to updated information on current runway surface conditions was thereby unnecessarily limited to reports from preceding aircraft.
The Probable Cause of the accident was determined to have been "the Captain’s inability to maintain directional control of the airplane due to his application of excessive reverse thrust, which degraded the effectiveness of the rudder in controlling the airplane’s heading".
Two Contributory Factors were also identified:
- the Captain’s situational stress resulting from his concerns about stopping performance
- the Captain's attentional limitations due to the high workload during the landing, which prevented him from immediately recognising the use of excessive reverse thrust.
Safety Action taken by Delta Airlines as a result of the accident included a reduction of normal reverse thrust for dry runways to 1.3 EPR and a new procedure for all non-dry runways requiring a mandatory initial use of idle reverse with a "methodical and gradual" increase to not more than 1.3 EPR permitted only after verification of both reverse thrust symmetry and alignment with the runway track. A re-formulation of landing distance tables using idle reverse thrust was also carried out and a "safety management system safety risk assessment" of the use of reverse thrust usage was initiated.
A total of 14 new Safety Recommendations were made at the conclusion of the Investigation as follows:
- that the Federal Aviation Administration should collaborate with Boeing and US operators of MD-80 series airplanes to:
- conduct a study to examine reverse thrust engine pressure ratio (EPR)-related operational data, procedures, and training and
- identify industry-wide best practices that have been shown to be effective in reliably preventing EPR exceedances to mitigate the risks associated with rudder blanking. [A-16-20]
- that the Federal Aviation Administration should encourage US operators of MD-80 series airplanes to
- implement the best practices identified in Safety Recommendation A-16-20 and
- participate in an industry-wide monitoring program to verify the continued effectiveness of those solutions over time. [A-16-21]
- that the Federal Aviation Administration should require operators of MD-80 series airplanes to revise operational procedures to include a callout when reverse thrust power exceeds 1.3 engine pressure ratio during landings on a contaminated runway. [A-16-22]
- that the Federal Aviation Administration should continue to work with industry to develop the technology to outfit transport-category airplanes with equipment and procedures to routinely calculate, record, and convey the airplane braking ability required and/or available to slow or stop the airplane during the landing roll. [A-16-23]
- that the Federal Aviation Administration should, if the systems described in Safety Recommendation A-16-23 are shown to be technically and operationally feasible, work with operators and the system manufacturers to develop procedures that ensure that airplane-based braking ability results can be readily conveyed to, and easily interpreted by, arriving flight crews, airport operators, air traffic control personnel, and others with a safety need for this information. [A-16-24]
- that the Federal Aviation Administration should require 14 Code of Federal Regulations Part 121 operators to provide:
- guidance that instructs flight attendants to remain at their assigned exits and actively monitor exit availability in all non-normal situations in case an evacuation is necessary and
- flight attendant training programs that include scenarios requiring crew coordination regarding active monitoring of exit availability and evacuating after a significant event that involves a loss of communications. [A-16-25]
- that the Federal Aviation Administration should develop best practices related to evacuation communication, coordination, and decision-making during emergencies through the establishment of an industry working group and then issue guidance for 14 Code of Federal Regulations Part 121 air carriers to use to improve flight and cabin crew performance during evacuations. [A-16-26]
- that the Federal Aviation Administration should clarify guidance to all 14 Code of Federal Regulations Part 121 air carriers to reinforce the importance of:
- having precise information about the number of passengers aboard an airplane, including lap-held children, and
- making this information immediately available to emergency responders after an accident to facilitate timely search and rescue operations. [A-16-27]
- that the Federal Aviation Administration should, for airports certificated under 14 Code of Federal Regulations Part 139, direct airport certification safety inspectors to ensure, before or during the airports’ next scheduled annual inspection, that policies and procedures for friction measurement during winter operations are accurately and adequately described in the airports’ Airport Certification Manual and Snow and Ice Control Plan. [A-16-28]
- that the Federal Aviation Administration should revise Advisory Circular 150/5200-30D, “Airport Field Condition Assessments and Winter Operations Safety,” to provide more precise guidance regarding (1) the need to issue notices to airmen (NOTAM) in a timely manner and (2) the specific changes to runway surface conditions that would prompt the issuance of updated NOTAMs. [A-16-29]
- that Boeing should collaborate with the Federal Aviation Administration and US operators of MD-80 series airplanes to:
- conduct a study to examine reverse thrust engine pressure ratio (EPR)-related operational data, procedures, and training and
- identify industry-wide best practices that have been shown to be effective in reliably preventing EPR exceedances to mitigate the risks associated with rudder blanking. [A-16-30]
- that Boeing should explore the possibility of incorporating an alert in MD-80 series airplanes to aid pilots in preventing engine pressure ratio exceedances. [A-16-31]
- that US operators of MD-80 series airplanes should collaborate with the Federal Aviation Administration and Boeing to:
- identify industry-wide best practices that have been shown to be effective in reliably preventing EPR exceedances to mitigate the risks associated with rudder blanking. [A-16-32]
- that the Port Authority of New York and New Jersey should, after consultation with the Federal Aviation Administration, clarify its policies regarding continuous friction measuring equipment use during winter operations and ensure that this information is included in the Airport Certification Manual and Snow and Ice Control Plan for each airport operated by the Port Authority. [A-16-33]
In addition, one previously issued (2009) Safety Recommendation was reiterated:
- that the Federal Aviation Administration should revise Advisory Circular 120-48, “Communication and Coordination Between Flight Crewmembers and Flight Attendants,” to update guidance and training provided to flight and cabin crews regarding communications during emergency and unusual situations to reflect current industry knowledge based on research and lessons learned from relevant accidents and incidents over the last 20 years. [A-09-34]
The Final Report was adopted by the Board on 13 September 2016 and subsequently published.