Boeing 737 N37437 and Airbus A320 N432UA accident near Sfo International Airport, California

Probable cause

the ramp controller directing a Boeing 737 to hold in a location that was marked for a regional jet.

NTSB analysis

On August 5, 2019, at about 2315 PDT, United (UA) flight 435, a Boeing B737-924ER, N37437, collided with UA flight 2201, an Airbus A320-232, N432UA, while taxiing to the gate after landing at San Francisco International Airport (SFO), San Francisco, California. There were no injuries to the passengers or crew on either airplane. The B737 sustained minor damage and the A320 sustained substantial damage. Both flights were operating as 14 Code of Federal Regulations Part 121 scheduled passenger flights. Flight 435 had arrived from Ellison Onizuka Kona International Airport at Keahole (KOA), Kailua-Kona, Hawaii, and flight 2201 arrived from Los Angeles International Airport (LAX), Los Angeles, California.

The captain of UA 435 stated that after landing, they were instructed by United G Ramp Tower (Ramp Tower) to hold at Plot 9, spot 11-1 to await a gate. When they arrived at the spot, UA 2201 was parked at spot 11-2 and another Airbus A320 was parked at spot 11-3. When UA 435 was cleared to taxi from spot 11-1, the captain noted that they were centered on their taxi line (11-1) and that UA flight 2201 was centered on their line (11-2). The captain ensured his left wingtip was clear of UA 2201 as he began to taxi and then turned his attention back forward to continue the taxi. A few seconds later, he felt a moderate bump and the nose pulled to the left. The captain stopped the airplane and set the parking brake and observed that their left winglet had struck UA 2201's right wing.

The Federal Aviation Administration (FAA) Principal Avionics Inspector (PAI) for United stated the distance between Spot 11-1 and Spot 11-2 was 100 feet. SFO airport operations marked the nose landing gear tire locations of both aircraft after the event and found that UA 2201 was parked 4 feet off the centerline, closer to spot 11-3, resulting in an effective distance between spot 11-1 and 11-2 of 104 feet. The wingspan of UA 2201's A320 was 117 feet and UA 435's B737 was 117 feet, so the provided spacing should have been over 117 feet to keep the wingtips from touching. The spacing between the centerlines for spot 11-1 and 11-2 was inadequate for UA flight 435 to have cleared the wing of UA 2201.

Examination of the pilot charts and Ramp Tower maps found differences for parking spots 11-1 through 11-3. The pilot chart depicted taxi lines that existed prior to restriping that occurred in March 2015. The old taxi lines, before restriping, had the centerlines of spot 11-1 and 11-2 further away from each other and would have given sufficient spacing for a B737 and an A320. The Ramp Tower's Procedures Manual identified the largest airplane allowed for parking Spot 11-1 was a "CRJ", which has a wingspan of about 76 feet. For Spots 11-2 and 11-3 the largest airplane indicated is a Boeing B757-300W. However, United Ramp Tower directed UA flight 435, a Boeing 737, to park on Spot 11-1.

Subsequent to the accident, the operator published a revised chart and sent an alert to pilots of the changes.

Text from the NTSB. Open the NTSB docket for DCA19CA192 for the full record.