What happened
On 03 May 2008, a Comair Limited Boeing 737-453, registration ZS-OAF, was preparing for a scheduled domestic flight from Cape Town International Airport to Port Elizabeth. During the pre-flight phase, the aircraft's Ground Power Unit (GPU) suddenly shut down. Because the Auxiliary Power Unit (APU) was inoperative at the time, this caused a significant interruption to the cockpit crew's electrical supply and workload.
During the takeoff roll on Runway 19, the pilot flying noted that the aircraft felt heavier and slower than usual in response to elevator inputs. As the aircraft reached rotation, the crew felt a physical bump, leading to the suspicion that a tail strike had occurred. The crew immediately retracted the landing gear and notified Air Traffic Control of the potential incident. After a runway inspection by the Fire Department, the aircraft was cleared to land. Upon returning to the airport, the crew discovered that the Air Speed Indicator (ASI) bugs had been set to speeds lower than those required by the takeoff card.
The investigation
SACAA AIID examined the flight data recorder (FDR) and the aircraft's physical condition. The investigation confirmed that the aircraft rotated approximately 1850 meters from the runway threshold. While the cockpit voice recorder (CVR) was unavailable due to being overwritten, the FDR provided critical data regarding pitch and rotation rates.
Physical inspection of the aircraft revealed that the tail-skid cartridge was partially compressed, with visible scrape marks on the skid shoe casting and damage to the associated fairing. However, no structural damage was found to the primary airframe, and there were no injuries to the 143 passengers or the 6 crew members on board.
Findings
- The primary cause of the incident was low speed during rotation due to the crew setting the Air Speed Indicator bugs incorrectly.
- A significant contributing factor was the sudden loss of electrical power from the GPU during pre-takeoff checks, which distracted the crew and interrupted their established procedures.
- The crew failed to verify that the ASI settings matched the takeoff card requirements following the power disruption.
- The aircraft's APU was not operational, which prevented the aircraft from maintaining electrical power via an alternative source during the GPU failure.