Introduction
On September 21, 2016, at approximately 1920 central daylight time, a Piper PA-30 airplane, registration N7663Y, was substantially damaged following a forced landing near Mineral Wells Airport (MWL) in Mineral Wells, Texas. The airline transport certificated pilot and one passenger sustained serious injuries, while another passenger was not injured. The personal flight was conducted under 14 Code of Federal Regulations Part 91 in visual meteorological conditions; no flight plan was filed.
Flight Details
The cross-country flight originated from Marfa Municipal Airport (MRF), Marfa, Texas, at 1655 and was en route to MWL. According to the pilot's written statements, he had earlier departed Draughon-Miller Central Texas Regional Airport (TPL), Temple, Texas, with all fuel tanks (main, auxiliary, and tip) full—a total of 114 gallons of usable fuel. After landing at MRF, 19.38 gallons of fuel were added; the pilot did not recall the distribution per tank but noted that no fuel was added to the tip tanks. He stated that on the flight from TPL to MRF, he used the tip tanks for about one hour and twenty minutes and the auxiliary tanks for an additional hour and ten minutes, using main tanks only for takeoff and landing. During the flight from MRF to MWL, he used only the auxiliary and main tanks, switching to main tanks after passing San Angelo, Texas, and remaining in that position.
Accident Sequence
While on approach to runway 13 at MWL, the pilot advanced the mixtures to rich about 7 to 10 miles from the runway. At that time, the right engine began to surge. He activated both electric fuel boost pumps and noted that fuel gauges appeared normal. He chose not to shut down the right engine. As he maneuvered for landing, the left engine also began surging. The airplane lost airspeed, and the pilot executed a forced landing in a clear area away from trees and obstacles.
Post-Accident Examination
The airplane was recovered to a hangar for examination under the National Transportation Safety Board, with assistance from an FAA inspector and investigators from Piper Aircraft and Lycoming Engines. The fuselage and wings were crushed and wrinkled; the empennage partially separated. Both tip tanks were impact-damaged and compromised, with no fuel recovered; damage was consistent with the tanks being full at impact. The right auxiliary and main tank bladders were intact with no breaches; one gallon of fuel was recovered from the right main tank fuel lines. The left auxiliary tank yielded three gallons of fuel, and its bladder was wet with a small amount of fuel. The left main tank showed no evidence of fuel. Fuel filters on both sides contained trace fuel with no visible contamination. The tip tank fuel lines held several ounces of fuel. No mechanical anomalies were found in the airplane fuel system that would have precluded normal operation.
Both engines were Lycoming IO-320-B1A. Examination of the left engine found spark plugs consistent with a lean state, white internal exhaust residue, no fuel in the main fuel line between the fuel pump and manifold, and no mechanical anomalies. The right engine showed similar lean signatures, trace fuel in the fuel servo, and no mechanical anomalies.
Aircraft Information
According to the Piper PA-30 Owner's Handbook (available in the accident airplane), the aircraft as equipped had 114 gallons of usable fuel. The manual stated that fuel should be used from the main fuel cells during takeoff, landing, climb, and descent; auxiliary and tip tank fuel was for level flight only. A placard above the fuel selector valves provided instructions for fuel selector valve handle and toggle switch placement.