B738 / E75L, San Diego USA, 2021

B738 / E75L, San Diego USA, 2021

Summary

On 10 June 2021, an Embraer 170-200LR was cleared to line up and wait on runway 27 at San Diego with a Boeing 737-800 already cleared to land on the same runway. The occupied runway led to ASDE-X activation which prompted a controller go-around instruction to the 737 when it was less than a mile from the runway displaced threshold but this was blocked by an undetected simultaneous transmission from the E170 which had just been instructed to exit the runway. The 737 manoeuvred around the E170 as it attempted to exit the runway, before touching down beyond it.

Event Details
When
10/06/2021
Event Type
AGC, HF, RI
Day/Night
Day
Flight Conditions
VMC
Flight Details
Type of Flight
Public Transport (Passenger)
Intended Destination
Take-off Commenced
Yes
Flight Airborne
Yes
Flight Completed
Yes
Phase of Flight
Landing
Flight Details
Operator
Type of Flight
Public Transport (Passenger)
Take-off Commenced
No
Flight Airborne
No
Phase of Flight
Taxi
Location - Airport
Airport
AGC
Tag(s)
Blocked Transmission
HF
Tag(s)
ATC clearance error, Distraction
RI
Tag(s)
ATC error, Incursion pre Take off, R/T Response to Conflict
Outcome
Damage or injury
No
Non-aircraft damage
No
Non-occupant Casualties
No
Off Airport Landing
No
Ditching
No
Causal Factor Group(s)
Group(s)
Air Traffic Management
Safety Recommendation(s)
Group(s)
None Made
Investigation Type
Type
Independent

Description

On 10 June 2021, a Boeing 737-800 (N8674B) being operated by Southwest Airlines on a scheduled domestic passenger flight from Phoenix to San Diego as SWA1648 had to deviate around an Embraer 170-200LR being operated by SkyWest on a scheduled domestic passenger flight from San Diego to San Francisco as SKW3371 which was on the runway prior to touching down. The 737 was cleared land but an instruction to go around was not received and the E170 was attempting to exit the same runway after being instructed to do so following an earlier line up and wait clearance on it.

Investigation

This Serious Incident was investigated by the US National Transportation Safety Board (NTSB). The 56 year-old 737 Captain had a total of 23,500 hours flying experience which included 14,500 hours on type and his 41 year-old First Officer had a total of approximately 8,000 hours flying experience which included 5,500 hours on type. Flying Experience for the 41 year-old Embraer Captain and his 30 year-old First Officer were not recorded. ATC radar and communications data were available, the latter from the Southern California TRACON with the radar source data obtained from sensors in San Diego.

What Happened and Why

Once the Southwest 737 crew had reported “field in sight, they were cleared for the RNAV ‘Z’ (RNP) approach to runway 27 which had a 2,314 metre LDA with a significantly displaced landing threshold. The First Officer was acting as PF. Once transferred to TWR when approaching a waypoint 13nm east of the runway 27 threshold, the flight was cleared to land and informed that there would be an aircraft on the runway awaiting departure. As they got nearer to the runway, the 737 crew saw the SkyWest E170 still on the runway at the beginning of the displaced threshold of the 2,866 metre-long runway 27. Their call to TWR querying its presence blocked a simultaneous transmission from the TWR instructing them to go around, so all they heard was an instruction not to overfly the E170.

The SkyWest E170 had been instructed to line up and wait on the full length of runway 27 and advised at that time that there was “landing traffic at 5 miles". They heard several other aircraft being cleared to land but no takeoff clearance was issued and the first instruction they heard was to exit the runway at the first available right hand exit which was C2. Eleven seconds after this instruction had been given, an ASDE-X alert of the still-occupied runway prompted the controller to transmit “Southwest sixteen forty-eight go around” as its crew simultaneously called “ah, is that an airplane on the runway for Southwest sixteen forty-eight”.

The recorded ATC audio captured the 737 Captain saying “ah,” followed by the controller transmitting “southwest sixteen forty-eight go around” followed immediately after this three second transmission by the 737 Captain saying “Southwest sixteen forty-eight” indicating that the two transmissions had blocked each other. The controller then said that the other aircraft was just exiting and not to overfly it so the 737 manoeuvred to the left to achieve this and then realigned with the runway centreline and touched down beyond it. As it subsequently did so, the controller transmitted “are you going around....” but according to the 737 crew this transmission “tailed off”. During the rollout, the controller then transmitted “I told you to go around” and received a response from the Captain who said they had not heard him say that, only not to overfly the aircraft.

The 737 touched down within the runway TDZ ten seconds after it had passed taxiway C2 at 200 feet agl (where the E170 was clear of the runway edge but not clear of the runway protected surface) occurred well beyond the exiting E170 since the latter had been within the initial takeoff only part of the runway at all times because of the 552 metre-long displaced landing threshold. The Investigation report gave the closest proximity of the two aircraft as 290 metres laterally and 200 feet vertically based on the position of the E170 when the 737 was approaching the end of the runway paved surface at 200 feet agl and the E170 which was about to clear the runway width at C2 but was still within the runway protected surface. Four seconds later, still at 200 feet agl, the 737 passed the C2 access link by which time the E170 was fully clear of the runway protected surface.  

B738&B75L_SanDiego_RWY27_linkC2

The beginning of runway 27 showing the displaced landing threshold and the C2 link. [Part of an illustration reproduced from the Investigation Docket]

The Investigation noted that FAA ATS procedures required that an aircraft status should not remain at ‘Line Up And Wait’ status for more than 90 seconds without additional instructions and that 107 seconds had elapsed between the E170 being instructed to line up and wait and being told to exit the runway.

The Probable Cause of the incident was formally documented as “the blocked go-around radio instruction from the air traffic control tower to the arrival aircraft which resulted in the arrival aircraft continuing the landing approach (and) led to a loss of separation between the landing aircraft and an aircraft (which had been) awaiting departure on the runway”.

A Contributory Factor was identified as the controller’s distraction (from the imminent conflict) communicating with a helicopter transitioning the airspace.

The Final Report was published on 7 September 2023. No Safety Recommendations were made. 
    
Editors Note: In view of the abbreviated nature of the Final Report, this Summary also referred to the corresponding Investigation ‘Docket’ (there is a link to it in the Final Report) through which the NTSB provides online access to information collected during the Investigation but not used in the published Report. This additional information has allowed some significant investigation findings not included in the Report to be incorporated in this Summary.

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