What happened
On September 9, 1997, at approximately 17:30 local time, a serious safety incident occurred at the intersection of two runways at Helsinki-Vantaa Airport. Two Finnair flights, MD-11 (OH-LGB) bound for Tokyo and DC-9-51 (OH-LYW) bound for Kemi, began their takeoff rolls almost simultaneously on intersecting runways 04 and 33.
The DC-9-51 was operating flight FIN-73, while the MD-11 was operating flight FIN-417. The tower controller, monitoring the takeoff of the DC-9-51, noticed that the MD-11 was also accelerating on the intersecting runway. To prevent a collision, the controller interrupted the takeoff of the MD-11, instructing the crew to stop. The DC-9-51 crew executed an aborted takeoff procedure, using maximum braking and reverse thrust. The aircraft decelerated and came to a halt well before the runway intersection.
The investigation
The investigation examined radio communications between the aircraft and the tower, as well as the sequence of clearances provided by ground and tower controllers. Investigators analyzed the cockpit procedures of the DC-9-51, noting that the crew had switched roles, with the captain acting as monitoring pilot and the first officer handling radio communications. The investigation also reviewed the technical state of the aircraft following the heavy braking, which resulted in significant heat buildup in the brakes and smoke from the tires.
Findings
- Overlapping radio transmissions were the primary cause of the incident. The tower controller issued a takeoff clearance to the MD-11 at the same time the DC-9-51 crew was acknowledging their own instructions. This simultaneous transmission prevented the controller from hearing the DC-9-51's readback.
>- The similarity in callsigns and runway numbers contributed to the confusion; the controller noted that the numbers '73' and '33' were visually and aurally similar in the context of the transmissions. >- The DC-9-51 experienced significant brake overheating during the aborted takeoff, with temperatures exceeding 700°C, leading to a blown thermal fuse and a loss of pressure in one tire. >- There was no inspection of the runway surface following the incident, despite ground controllers reporting visible smoke from the aircraft's tires.