Created Thursday, Oct 20th 2022 19:18Z, last updated Tuesday, Jul 30th 2024 15:45Z
An Euro Atlantic Airways Boeing 767-300, registration CS-TKR performing flight STP-507 from Sao Tome (Sao Tome and Principe) to Lisbon (Portugal) with 223 passengers and 14 crew, was departing Sao Tome's runway 11 when past V1 (126 KIAS) and before Vr (136 KIAS) the #2 engine (CF6) suddenly and rapidly lost thrust, all parameters dropped. The crew climbed out to FL100, shut the engine down, entered a hold to dump fuel and returned to Sao Tome for a safe landing on runway 29 about 2:40 hours after departure.
In October 2022 Portugal's GPIAA reported that the investigation carried out by the National Accident Investigation Commission of Sao Tome and Principe concluded the power loss was caused the failure of the #2 HMU.
Sao Tome's INAC released their final report concluding the probable cause of the serious incident was:
The cause of the engine power loss was failure of the HMU.
CONTRIBUTORY FACTORS
AFSO solenoid grommet raised and out of position, which led to insufficient fuel flow.
Escaping pressure on P2P tube connected to the Over Speed Bracket Assembly adversely affected the Head Sensor Assembly causing excessive Bypass valve opening and associated drop in fuel flow.
Ground wires for the Resolvers were backed out from their normal installed position in the connector.
The INAC analysed:
On the day of the occurrence, STP Airways Fight 8F 508 to Lisbon with 237 persons on board (223 pax plus 14 crew members) was within schedule time.
After boarding passengers and having performed all related flight checks and procedures, the aircraft was cleared and authorized to taxi to the take off position for departure rwy 11.
During take off run, the aircraft after the V1 (126 kt) and just before the rotation speed (144 kt) when passing through 136 kt, the engine #2 had a sudden and rapid thrust reduction and drop in all parameters.
At that stage the crew continued the take off to a safe recommended altitude to be able to assess and determine the probable cause of engine # 2 loss of power.
During the event the crew took all necessary action to mitigate the abnormal situation and performed the procedures in accordance with NCC (Non Normal Checklist-Engine Limit/Stall), SOPS and Checklists. CRM among pilots were good.
On the ground, troubleshooting and borescope inspection were carried out on engine #2 with no findings of any damage. It was found that the malfunction of hydro mechanical unit caused the loss of power of the # 2 engine.
The Unit was sent to a certified shop to identify the cause of failure. With the work accomplished it was concluded that reason for the failure of HMU was due to solenoid grommet raised and out of position and as well the escaping pressure on P2P tube connected to the Over Speed Bracket Assembly adversely affected the Head Sensor Assembly causing excessive Bypass valve opening and associated drop in fuel flow.
