B772 / B739, New York JFK USA, 2023
B772 / B739, New York JFK USA, 2023
On 13 January 2023, in good night visibility, an augmented crew Boeing 777-200 failed to comply with its departure taxi clearance and with its Captain taxiing crossed a runway in front of a 737 taking off. ATC responded to an automated conflict warning by cancelling the takeoff clearance and a high speed rejected takeoff was initiated from approximately 105 knots with minimum separation as the 777 cleared the edge of the 737 takeoff runway approximately 300 metres. The Investigation concluded that the 777 operator’s risk controls and the airport’s methods for detecting and preventing dangerous runway conflicts were both inadequate.
Description
On 13 January 2023, a Boeing 777-200 (N754AN) being operated by American Airlines on a scheduled international passenger flight from New York JFK to London Heathrow as AAL106 failed to comply with its departure taxi clearance and crossed an active runway in front of a Boeing 737-900 (N914DU) being operated by Delta Airlines on a scheduled international passenger flight from New York JFK to Santo Domingo as DAL 1943 which was taking off as cleared. An automated alert prompted ATC to cancel the 737s takeoff clearance and as the 777 completed its unauthorised crossing, the minimum separation as the 737 decelerated was approximately 300 metres.
Investigation
The NTSB “learned about this event” the following day and an Investigation was carried out by the NTSB using relevant data successfully downloaded from the FDRs of both aircraft. Relevant data from both CVRs was overwritten but relevant recorded data from the ASDE-X system and from all relevant ATC radio and telephone communications were available.
It was noted that the 61 year-old 777 Captain had been employed by American Airlines for 33 years and had a total of 20,041 hours flying experience which included “about 9,000 hours” on type of which “about 500 hours” was in command following promotion to Captain on type 11 months prior to the event under investigation. He stated that he had been based at JFK for “about 10 years” and was “very familiar” with the airport. The 52 year-old First Officer had a total of 11,250 hours flying experience and had been employed by American Airlines for almost 9 years during which she had recorded a total of just 1,188 hours flying experience for the airline of which “about 126 hours” had been on type. The Relief First Officer had been employed by American Airlines for 6½ years and had since recorded 2,854 flight hours for the airline of which “about 110 hours” had been on type. He reported being familiar with JFK having operated there for a previous employer.
The 61 year-old 737 Captain had been employed by Delta for almost 24 years and had 11,453 hours flying experience including 2,906 hours on type. After serving as a DC9 First Officer, he had transferred to the 757/767 fleet as First Officer before promotion to 737 Captain during 2018. The 33 year-old 737 First Officer had been employed by the airline for seven months during which he had recorded 203 hours on type.
It was noted that the 777 flight crew did not report the incident to American Airlines before departure with the Captain stating that he was unaware of any provision in the OM that would have prohibited the flight’s departure following the incursion.
What Happened
Whilst the 777 Relief First Officer was performing the external pre-flight check, the operating crew reported having completed a preliminary departure brief based on an anticipated departure from runway 31L. On the basis of the ATIS current at the time, the Captain subsequently “recalled that his briefing had included taxiway ‘A’, left on ‘B’ and hold short at ‘J’, which he stated was the standard route to runway 31L from the American Airlines gates at the airport”. The First Officer “stated that the airport diagram was available and was referenced during these discussions”. The Captain also recalled subsequently telling the Relief First Officer to speak up if he had any safety concerns. The First Officer was designated as PF for the sector but in accordance with applicable company procedures, the Captain would be taxiing the aircraft onto the departure runway.
The clearance subsequently received by ACARS was for a runway 04L departure so the latest ATIS was checked, the FMS reprogrammed and the departure and taxi route re-briefed. According to the First Officer, the Captain’s revised taxi briefing stated, “same taxi route up until Bravo short of Kilo”. The Captain recalled (correctly) briefing both First Officers that the controller would “have you come up Kilo, and then as you get closer, they’ll tell you when to cross [runway 31L]” and added that “this was the typical route from the American Airlines gates to runway 04L”. The illustration below shows the flight’s taxi route from the gate to runway 04L as cleared and the subsequent deviation from it.
The assigned (broken orange line) and actual (solid orange line) taxi routes for the departing 777 overlaid on a satellite image of the relevant part of the airport. [Reproduced from the Official Report]
The initial taxi clearance given to the 777 by the GND controller was as anticipated by the Captain - “taxi to runway 04L via a left turn onto taxiway ‘B’ and to hold short of taxiway ‘K’”. Seven minutes later, as the aircraft was on taxiway ‘B’ approaching taxiway ‘N’, the same controller instructed the flight to cross runway 31L at taxiway ‘K’. Both these clearances were read back correctly. Shortly after this, the 04L TWR controller instructed the 737 to line up and wait on runway 04L advising that there would be traffic crossing right to left.
The 777 Captain subsequently stated that he had been “discussing aircraft performance values with the First Officer” as the aircraft approached taxiway ‘K’. As the TWR controller cleared the 737 for takeoff, the 777 crossed taxiway ‘K’ and began to turn left onto taxiway ‘B’, which curved to the left (see the illustration below). The GND controller subsequently stated that he had seen the 777 “swing out to the left on taxiway ‘B’ to begin what he believed to be a typical wide right turn onto taxiway ‘K’” but since the crew had correctly read back the clearance given, “he had expected them to adhere to the instructions and perform the taxi route as assigned”.
The area of taxiways ‘B’, ‘K’, and ‘J’; and runways 4L and 31L with the 777’s assigned (dashed orange line) and actual (solid orange line) taxi routes overlaid. [Reproduced from the Official Report]
Fifteen seconds after the 737 had been cleared for takeoff, the 777 made a right turn onto taxiway ‘J’ and continued past the runway 04L holding point and onto the runway. The First Officer subsequently stated that she had been “head-down” and talking about takeoff performance when she heard the Captain say, “cleared to cross?” and had looked up, checked the runway and final approach to the right without seeing an aircraft on the runway and, “according to all three pilots”, the Captain had then called “clear left” and the First Officer had called “clear right.”
ADS-B data indicated that the 737 had begun its takeoff roll on runway 04L ten seconds before the 777 began to cross runway 04L holding point at a groundspeed of about 11 knots. The ASDE-X indicated that at this time, the RWSL system Runway Entrance Lights (RELs) had illuminated and the 737 was 1,189 metres away and accelerating through 47 knots. Ten seconds later, as the nose of the 777 entered the runway, the 737 was 823 metres from the intersection and accelerating through 94 knots ground speed. The 777 Captain subsequently stated that as the aircraft had begun to cross the runway he had “seen red lights illuminate on the runway but was unsure why they had illuminated and chose to add power to expedite the runway crossing”. The First Officer subsequently stated that she had “also observed red lights illuminate (and) that they did so after the aircraft crossed the runway holding point”. The Relief First Officer subsequently stated that he was “head-down” as the aircraft had approached the runway and after hearing “some confusion about crossing a runway", he had looked up and seen “another aircraft down to the right” and (according to the Captain) had stated that another aircraft was “taxiing on the runway.” This reportedly prompted him to look to the right and see an aircraft that “appeared to be taxiing on runway 4L (which) did not look that close from his perspective”.
Recorded ATC communications showed that after issuing the 737s takeoff clearance, the TWR controller spoke with two other aircraft which were taxiing for takeoff and was still doing so when the ASDE-X system annunciated a “runway occupied” alert 12 seconds after he had issued the clearance. He responded after five seconds by calling the 737 to say that their takeoff clearance was cancelled and in the absence of an immediate response repeated this call four seconds later, receiving an acknowledgement from the 737 three seconds later. FDR information from the 737 showed that they were initiating their rejected takeoff as the second controller call was being made. Three seconds later, the 737 reached a maximum groundspeed of 105 knots with just over 700 metres to go until reaching the point where the 777 was obstructing the runway. As the 777 cleared the runway nine seconds later, at a groundspeed of 21 knots, the 737 was decelerating through a groundspeed of 49 knots with just over 300 metres to go before reaching the previously obstructed intersection.
Shortly afterwards, the TWR controller asked the 737 if they were able to taxi or if they needed to complete checks and having received confirmation that they could clear the runway instructed it to turn left onto the western part of taxiway ‘J’. The 777 flight crew did not hear this exchange as they were still on the GND frequency but they subsequently stopped on the eastern part of taxiway ‘J’ and changed to the TWR frequency where they were told that “they had a possible pilot deviation and to stand by for a phone number”. The 777 Captain then asked if they had been cleared to cross and the controller replied that “we’re departing runway 04L (and) you are supposed to depart runway 04L (but) you are currently holding short of Runway 31L”. The Captain subsequently stated that “he realised during this discussion that he had made a mistake”.
The GND controller subsequently stated that although he had not transferred the 777 to TWR, he “had not known if the 777 crew were monitoring his frequency” and that when he saw the aircraft was crossing 04L, he had “decided it was best to let it continue crossing (as he had felt that) broadcasting the 777s callsign may have caused the crew to slow down or stop”.
Why It Happened
Neither the operating nor relief First Officers’ noticed the Captain’s failure to taxi as instructed and the RELs did not provide a timely effective direct alert to the 777 flight crew. The Investigation therefore looked in detail about why this had been so.
It was noted that the airport was one of 20 US airports with RWSL systems installed to provide an indication of runway incursion risk directly to pilots. It was further noted that all RELs ahead of a departing aircraft are designed to illuminate when that aircraft passes 30 knots ground speed and each set will then extinguish “approximately 2 to 3 seconds before the aircraft reaches it” to allow controllers to apply “anticipated separation” and allow other traffic to “move more expeditiously without compromising safety”. Once an aircraft is classified as ‘airborne’ by the RWSL system, all its lights will then extinguish.
A playback file of the ASDE-X taxi paths for the two aircraft were compared with the ADS-B positions transmitted by both aircraft and although broadly consistent, the airplane symbols shown on the ASDE-X replay corresponded to the position of the wings rather than the location of the aircraft GPS antenna which meant that in both cases, the aircraft nose appeared to be slightly ahead of the probable actual position.
The ASDE-X replay actually indicated that the RELs had only illuminated as the 737 was accelerating through 48 knots groundspeed. The illustration below shows a scaled depiction of the 777 at this time “with its GPS antenna location positioned at the ADS-B GPS position point” and the nose just crossing the holding point at a ground speed of 11 knots with the first REL already beneath the aircraft. It was calculated that the 777 pilots would have been able to see RELs which were at least 25 metres in front of the airplane’s transmitted GPS location. The ASDE-X aircraft location is within ± 3 metres so with all the RELs illuminated, four of the six red lights would have been “within the crew’s field of view” and the second one “may have been”. At the taxing speed of the 777, the final REL would have passed out of view after about 12 seconds (and would all have been turned off 15 seconds later as the 737 speed reduced below 25 knots). However, the ASDE-X replay of the event indicated that the second REL was “extinguished” and the third REL was “faulted”. As the responsible ANSP, FAA requirements for RWSL system maintenance were found to state that “operational tolerance/limits allow for <50% of the lamps in an REL array to be inoperative”.
However, it was concluded that whilst the RELS had operated “as designed” and in accordance with applicable maintenance requirements, they had not been effective in preventing the aircraft from crossing the runway holding point. On the other hand, it was considered that controller’s timely response to the ASDE-X alert and the 737 crew’s prompt reaction when instructed to stop “likely reduced the severity” of the occurrence.
The 777 at the 04L/’J’ intersection relative to the RELs as it crossed the holding point. [Reproduced from the Official Report]
Turning to the origin of the conflict, the Investigation considered why the 777 crew had made such a significant and dangerous error. It was concluded the Captain’s deviation from the accepted taxi clearance was likely to have been attributable to several factors including:
- an early clearance to cross runway 31L,
- interruptions and multitasking related to a delayed receipt of the load closeout whilst taxiing,
- his prospective memory error in forgetting to turn right at taxiway ‘K’,
- environmental capture, which led to him following a familiar, but incorrect, route.
In respect of the failure of both the operating and relief First Officers to notice the error made, it was surmised that both had become distracted from their primary duty of assisting the Captain to safely taxi the aircraft after completely losing situational awareness and failing to focus on monitoring compliance with the accepted taxi clearance by prioritising other, less critical, activity. It was further surmised that the operating First Officer’s failure to see the approaching 737 when looking along the runway before declaring that it was “clear right” had probably been influenced by expectation bias and the absence of recognisable relative motion of the 737.
It was, as in a number of previous NTSB Investigations, noted that the absence of a CVR with a 25 hour recording capability had resulted in potentially useful information in respect of intra crew communication being lost and only ‘recollections’ of such interaction being available.
The Probable Cause of the conflict was determined as "the American Airlines flight 106 crew’s surface navigation error due to distractions caused by their performance of concurrent operational tasks during taxi, which resulted in a loss of situational awareness”.
Three Contributory Factors were also identified as follows:
- The air traffic control tower team’s non-detection of the 777 crew’s deviation from taxi instructions while performing concurrent operational tasks;
- the timing of the Runway Status Light System, which activated too late to prevent the 777 crew from crossing the runway hold short line;
- American Airlines’ lack of adequate risk controls to prevent concurrent flight crew tasks from leading to distraction, loss of situational awareness and deviation from an authorised taxi clearance.
Eight Safety Recommendations were made based on the Findings of the Investigation as follows:
- that the Federal Aviation Administration encourage Title 14 Code of Federal Regulations Part 91K, 135, and 121 operators to incorporate into their standard operating procedures a procedural crosscheck that requires flight crews to verbalise the number of a runway they are about to cross, as indicated by runway signs, unless an installed automated system already provides an aural advisory. [A-24-2]
- that the Federal Aviation Administration encourage Title 14 Code of Federal Regulations Part 121 operators to use their safety management system to identify flight crew surface navigation errors resulting from the performance of concurrent tasks during taxi and develop and implement effective risk mitigation strategies considering human factors principles. [A-24-3]
- that the Federal Aviation Administration collaborate with aircraft and avionics manufacturers and software designers to develop the technology for a flight deck system that would provide visual and aural alerts to flight crews of traffic on a runway or taxiway and traffic on approach to land. [A-24-4]
- that the Federal Aviation Administration require that the technology developed in response to Safety Recommendation A-24-4 be installed in all newly-certificated transport category aircraft. [A-24-5]
- that the Federal Aviation Administration require that existing transport category aircraft be retrofitted with the technology developed in response to Safety Recommendation A-24-4. [A-24-6]
- that the Federal Aviation Administration evaluate the effectiveness of the activation logic for the runway status light system considering the circumstances of this incident. [A-24-7]
- that the Federal Aviation Administration, using the findings of the evaluation conducted in response to Safety Recommendation A-24-7, update the Runway Status Light System activation logic as necessary to improve system effectiveness. [A-24-8]
- that the Federal Aviation Administration require retrofit of all Cockpit Voice Recorders (CVR) on all aircraft required to carry both a CVR and a flight data recorder with a CVR capable of recording the last 25 hours of audio. [A-24-9]
The Board also reviewed previous related safety recommendations which it had issued and remarked in this Final Report as follows:
- Safety Recommendation A-18-30 which invited the Federal Aviation Administration to require that “all newly manufactured airplanes that must have a cockpit voice recorder (CVR) be fitted with a CVR capable of recording the last 25 hours of audio" was reiterated.
- Safety Recommendation A-00-66 is classified as ‘Closed – Unacceptable Action’ and superseded by the issue of Safety Recommendations A-24-4, A-24-5 and A-24-6 which are classified ‘Open - Unacceptable Response’.
- Safety Recommendation A-18-31 is classified ‘Closed – Unacceptable Action’ and superseded by the issue of Safety Recommendation A-24-9, which is classified ‘Open - Unacceptable Response’.
The Final Report was completed on 29 May 2024 and published online the following month.