What happened
On November 27, 2012, at approximately 1558 CST, an MD 500D (Hughes 369D) helicopter, registration N28MP, experienced a loss of engine power while performing long-line power line construction near Childress, Texas. The aircraft was engaged in an external-load operation, hovering 120 to 150 feet above the ground to allow a long-line worker to attach travelers to a transmission tower.
During the stable hover, the helicopter experienced a sharp left yaw, which the pilot initially attributed to a wind gust. Within milliseconds, the engine began to wind down. The pilot observed the engine-out annunciation and attempted to move the aircraft away from the tower to avoid a collision. As the helicopter descended, the long-line worker was pulled off the tower by the momentum of the 50-foot long-line. The pilot attempted an autorotation, but the helicopter impacted the terrain in a right-side-low attitude. The collision resulted in 1 fatal injury to the long-line worker and 1 serious injury to the pilot. The aircraft sustained substantial damage.
The investigation
Investigators found that the helicopter contained no usable fuel, and the quantities found between the fuel tank and the engine were consistent with fuel exhaustion.
Examination of the fuel system revealed that the electrical wire for the start pump was not secured, which allowed it to interfere with the fuel quantity transmitter float mechanism. This interference caused the cockpit fuel gauge to provide erroneous indications to the pilot. Additionally, the low fuel quantity annunciator was inoperative because the fuel quantity transmitter's low-level fuel whisker had separated due to fatigue and overstress.
Maintenance records showed that the operator's mechanic had recently replaced the start pump and tested the low-level fuel light by grounding the transmitter with safety wire. However, the mechanic did not perform a vacuum check of the fuel system after the system had been opened, which was required by the maintenance manual. The investigation also noted a nonstandard installation of a petcock drain valve on the engine-mounted fuel filter.
Findings
- The pilot's fuel management was inadequate, as he relied on fuel gauge indications that were inaccurate due to mechanical interference.
- The improper maintenance of the fuel system led to erroneous fuel gauge readings and an inoperative low-fuel warning light.
- The lack of company procedures for tracking fuel loading and time-based consumption prevented the pilot from identifying the discrepancy between the gauge and actual fuel levels.
- There were no written company procedures to ensure adequate maintenance and fuel planning.