N574HEnstrom F-28C · 1976

On December 7, 2012, about 1545 central standard time, an Enstrom F-28C helicopter, N574H, impacted terrain during an autorotation following a loss of engine power during approach to the Abilene Regional Airport (ABI), near Abilene, Texas. The certified flight instructor and student pilot reported no injuries. The helicopter sustained substantial tailboom damage. The helicopter was registered to and operated by the student pilot under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual flight rules (VFR) conditions prevailed for the flight, which did not operate on a VFR flight plan. The flight originated from the Brownwood Regional Airport (BWD), near Brownwood, Texas, at time unknown and was destined for ABI.

According to the flight instructor’s accident report, the instructor and student pilot arrived at 0930 outside a fixed base operator at the ABI. They discussed subjects including his helicopter; N574H, helicopter logbooks, maintenance history, helicopter airworthy condition, preflight actions, the student pilot’s aviation experience, and various other topics for about an hour. There were no pending maintenance issues detected and after an extensive preflight inspection, the instructor found the helicopter to be in an airworthy condition. The instructor indicated that the fuel tanks were completely filled, which would have given them “40 gallons of total fuel.” The student requested that they fly to Albany, Eastland, Brownwood then return to Abilene. The first three legs were uneventful with landings at all three locations. On the last leg, he noted the fuel level and made the decision to continue to ABI. The fuel gauge read 3/8ths full. The instructor estimated that out of 40 gallons total fuel, the helicopter passed over BWD with 15 gallons of fuel. He further figured that with a fuel burn of 13.5 gallons per hour and 30 to 35 minutes to ABI, the helicopter should land with the required 20-minute reserve. Approximately four miles from ABI, the flight was cleared to pass behind a Beechcraft on final to 17L. At 2 miles from ABI, the helicopter yawed left briefly. The instructor stated that he turned his attention from the Beechcraft to the engine instruments and to what the student pilot was doing. The helicopter yawed to the left one more time and the engine and rotor RPM began to decay. The instructor lowered the collective, let the student pilot know that he was now flying the helicopter, and leveled the helicopter for a 70-knot attitude. This made the rotor RPM decay even further, where it was now under the minimum for autorotative descent. The instructor pushed the nose over then back to nose level. He reported this caused the blades to cone upward and increase rotor RPM, but it was still below the red line. The instructor nosed the helicopter over again and turned left. This caused the rotor to cone upward and “unload”. He said that this maneuver should have regained “rotor speed to the high side but was only slightly effective.” The instructor, in part, reported:

It was now fairly certain to me that I was not only having an

engine failure, but also the over running clutch had not

disengaged the engine from the transmission. I was now facing

to the South and rotor RPM at the red line once again. I flared

the helicopter at 30 feet AGL [above ground level]. This slowed

the helicopter down but now the rotor system was “loaded” and

being dragged down to 200 RPM. At 3 feet I leveled the

helicopter and applied collective to cushion the landing but I

had only about 1/3rd of the rotor RPM normally available. The

helicopter landed level with very little forward movement. One

of the main rotor blades contacted the tailboom causing the

helicopter to spin to the left approximately 60 degrees. The

next rotor blade contacted to tailrotor debris. The third main

rotor blade had only the damage caused by the sudden stoppage.

According to the student pilot’s accident report, the student pilot voiced his opinion on the low fuel quantity on board the helicopter. He said that the flight instructor informed him the fuel gauges are often faulty and that they had enough fuel to complete the return leg of the flight to ABI.

Federal Aviation Administration inspectors oversaw a postaccident examination of the helicopter. A mechanic assisted the inspector’s examination where less than one gallon of fuel was drained from each of the right and left hand fuel tank sumps. The fuel strainer and fuel injection servo screen were examined and reinstalled. The helicopter was serviced with four gallons of 100 low lead aviation gasoline. The engine subsequently started and ran smoothly for five minutes. An inspector examined the over running clutch operation and no anomalies were detected.

The Enstrom rotorcraft flight manual (FM) for the F-28C helicopter preflight inspection checklist indicated that the right hand and left hand fuel tanks are to be visually checked in reference to their quantity and confirm both fuel tank caps are secured. The checklist further indicated to drain both the right hand and left hand tank sumps. The FM, in part, stated:

Maximum: ............................ 385 rpm

Minimum .............................. 332 rpm

...

4. Gently close throttle to split tachometer needles to check

proper operation of over running clutch.

...

1. Enter normal autorotation and stabilize at 58 MPH (minimum

rate of [descent]). (See Height Velocity information, pages FM-

5-4 and FM-5-5.)

NOTE: Due to high rates of descent at forward speeds, sustained

auto rotation speed is limited to 85 MPH to

8200 ft. Above 8200 ft., see FM-5-1.

Maximum glide distance in autorotation is attained

at 80 mph and 332 rotor rpm. (Reduce collective to

build RPM prior to touchdown.)

At 1452, the recorded weather at ABI indicated that the wind was calm.

Enstrom Service Directive Bulletin No. 0092, Fuel Quantity System Calibration, indicated that one gallon per fuel tank was unusable fuel and in part, stated:

Pilots can assist in determining if the fuel quantity system is

operating correctly by monitoring the fuel quantity indication

prior to and after refueling and comparing the indications to

the total quantity of fuel used in servicing the tanks. In

addition, a fuel dipstick, [part number] 28-12478-11 for all

20 gallon (40 gallon total capacity) tanks, should be used

during preflight inspection to verify fuel quantity on all

aircraft so equipped.

Neither the flight instructor nor the student pilot visually checked the fuel level in the fuel tanks at any of the stops during the round robin cross-country flight.