The Inhofe Accident

The NTSB wished for more facts about what Senator Inhofe’s son faced

There has been no stronger advocate on Capitol Hill for general aviation and the pilot community than Senator James Inhofe, Republican, of Oklahoma. A pilot for more than 50 years, with more than 10,000 hours logged, he shaped legislation to benefit GA, including the Pilot's Bill of Rights. It was designed to counteract the entrenched FAA policy that pilots are guilty until they can prove themselves innocent and must do so without benefit of the FAA's evidence.

pr Senator Inhofe's involvement in aviation makes it doubly tragic that his son, Dr. Perry Inhofe, age 51, was killed in the crash of the Mitsubishi MU-2B-25 twin turboprop he was flying on November 10, 2013. In October 2014, the NTSB determined that the probable cause of the accident was Dr. Inhofe's loss of aircraft control during an engine-out situation. However, it couldn't explain why he lost control or why the engine was out. Just as Senator Inhofe's legislation expressed displeasure with the FAA for declaring pilots as guilty until proven innocent, the Safety Board's report on his son's accident expressed displeasure with the FAA for not requiring recording devices that might have answered questions about what Dr. Inhofe was facing.

The accident occurred at about 3:46 p.m., in wooded terrain near Owasso, Okla., about five miles from Tulsa International Airport, at an elevation of about 650 feet. Dr. Inhofe was the only person onboard. Visual meteorological conditions prevailed, and the airplane was on an IFR flight plan. The flight departed Salina Regional Airport (SLN), Salina, Kan., at about 3:03, and was en route to Tulsa International Airport (TUL), Tulsa, Okla.

At 3:34:09, Dr. Inhofe contacted Tulsa Approach, reporting being out of 11,600 feet for 10,000 feet. He said he had ATIS information Charlie. The controller advised the pilot to expect vectors for a visual approach to runway 18L, and Dr. Inhofe acknowledged. At 3:37:46, the controller called for a turn 10 degrees left and descent to 6,000 feet. At 3:40:07, the controller asked the pilot to turn another 10 degrees left and instructed him to descend to 2,500 feet. The pilot acknowledged.

At 3:42:04, the controller advised that the airport was at one o'clock and 10 miles, and asked the pilot to report the airport in sight. Dr. Inhofe immediately replied, "In sight." He was cleared for a visual to runway 18L and was told to call the Tulsa tower.

At 3:42:20, Dr. Inhofe came up on the tower frequency. The controller cleared him to land and asked him to reduce speed to 150 knots or less for spacing behind an aircraft that would be departing from runway 18L. Dr. Inhofe replied that he was reducing speed.


After passing the runway 18L outer marker, the MU-2B began a left turn. At 3:44:48, when the airplane was about 90 degrees from the runway approach path, the tower controller transmitted, "Mitsubishi six Juliet tango tower." Dr. Inhofe replied, "I've got a control problem." The controller responded, "Okay, uh, you can just maneuver there if you can maneuver to the west, and uh, do you need assistance now?" At 3:45:06, Dr. Inhofe radioed, "I've got a left engine shutdown."

At 3:45:11, the tower controller contacted the approach controller on the interphone system to advise of the problem and that other aircraft might have to be cleared out of the area.

At 3:45:38, the tower controller transmitted, "Six Juliet Tango, are you, uh, declaring an emergency; uh, well, we'll declare emergency for runway 18L; you say you have an engine out and souls on board and fuel remaining, if you have time." There was no response to that transmission and no response when the controller tried two more times.

Radar data showed the airplane completing a 360-degree left turn near the runway 18L outer marker at 1,100 feet MSL. After that, radar contact was lost.

Seven witnesses saw the airplane in a shallow left turn. They variously reported the altitude as 400 to 800 feet. Four witnesses said the landing gear was extended. Two said one propeller appeared not to be rotating or was slowly rotating. One witness reported seeing black exhaust following the airplane, but four witnesses reported not seeing any smoke. Some witnesses said the wings rocked left and right at a 10- to 15-degree bank angle. Then they said the airplane was in a bank to the right, followed by a hard bank to the left. Some of the witnesses observed the airplane spiral toward the ground and disappear from view.

Dr. Inhofe held a commercial certificate and was a flight instructor. His third class medical certificate was current with no limitations. His medical application indicated no use of medications and no medical history conditions.

Although his pilot logbooks were partially consumed by fire, investigators found sufficient documentation to establish that he had at least 2,874 total flight hours with 1,534 in multi-engine airplanes. Most of his multi-engine time was in a Cessna 421B, which he owned since 2010.

Investigators interviewed three pilots who flew with Dr. Inhofe in the months before the accident. They described him as a very good aviator who meticulously followed checklists. None of the interviewed pilots recalled the pilot displaying any negative or bad flying habits.

The FAA has a Special Federal Aviation Regulation (SFAR 108) that requires MU-2B pilots to have special training, experience and abide by special operating conditions. Pilots can't act as pilot-in-command (PIC) of an MU-2B unless they've logged at least 100 flight hours as PIC in multi-engine airplanes. They also need at least 20 hours of ground instruction and a minimum of 12 hours of flight instruction in the MU-2B.


Dr. Inhofe had completed MU-2B training at a school in Salina, Kan., on the morning of the accident. He received individual instruction and spent 32 hours in ground school. He satisfactorily completed required checks and received an SFAR endorsement in the MU-2B-25. The accident flight from SLN to TUL was the first time Dr. Inhofe flew as a single pilot in the MU-2B-25 airplane.

Dr. Inhofe flew three training flights during which landing configuration stalls were performed. In addition, he performed a landing configuration stall maneuver during his final phase check flight.

The high-performance, twin-engine, high-wing turboprop was manufactured in 1973. It was registered to the current owner on September 26, 2013. Investigators determined that a combined 100 hour/annual inspection was completed on September 19, 2013, at a total airframe time of 6,581.4 hours (about 12.9 hours before the accident flight). The engines had accumulated 936.4 hours since overhaul.

The main wreckage area held all major airplane structures and components. Post-impact fire consumed a majority of the fuselage and wing structure. The left engine propeller blades were found in a feathered position.

An airspeed study indicated that the airplane was operating close to the 20-degree flaps, one-engine inoperative minimum controllable airspeed (Vmc) of 93 knots calibrated airspeed (KCAS) during the time that Dr. Inhofe reported control and engine problems. In addition, the calculations indicated that the final descent of the airplane into the ground followed an aerodynamic stall of the wing. This finding was consistent with the condition of the wreckage, its location very close to the last radar point, and witness statements.

Also, by 3:44:15, the airspeed had already decayed to around 95 KCAS, close to the Vmc with flaps at 20 degrees of 93 KCAS. The airplane may have been easier to control at lower power settings on the operating engine, but may still have presented a challenging situation to the pilot, given the low energy state of the airplane and its proximity to the ground.

The NTSB report suggested that during the final 360-degree left turn, the highest priority to ensure the safety of the flight would have been to increase the control margin by increasing the airspeed further above the 93 KCAS Vmc speed. However, to increase the speed, a pilot would have to increase power on the operating engine, thereby making thrust asymmetry worse. An alternative would be to trade altitude for airspeed, which Dr. Inhofe probably was reluctant to do being five miles or so from the airport. A pilot could also increase the speed and margin by retracting the landing gear, thereby lowering the airplane's drag. Investigators determined the power was increased between 3:44:10 and 3:44:30, when the airplane was already in a difficult situation because of the combination of low altitude, low airspeed and the reported problem with the left engine.


The NTSB noted that the airplane wasn't required to have any type of crash-resistant recorder installed. Previous NTSB recommendations to the FAA have addressed the need for recorders on airplane types like the MU-2B. The Safety Board has told the FAA that recorders can help investigators identify safety issues that might otherwise be undetectable, which is critical to the prevention of future accidents.

...The probable cause of the accident was the pilot's loss of airplane control during a known one-engine-inoperative condition.

On May 6, 2013, the NTSB had issued Safety Recommendation A-13-13. It called on the FAA to require all existing turbine-powered, nonexperimental, nonrestricted-category aircraft that aren't equipped with a flight data recorder or cockpit voice recorder and are operating under Parts 91, 121 or 135 to be retrofitted with a crash-resistant flight recorder system. The crash-resistant flight recorder system should record cockpit audio and images with a view of the cockpit environment to include as much of the outside view as possible.

The FAA's response was that it had not found any compelling evidence to require installation of cockpit recording systems as recommended. The FAA told the NTSB that it planned no further action to mandate flight deck recording systems and considered its actions complete. On December 10, 2013, a month after the Inhofe accident, the NTSB declared the FAA's response to be "unacceptable."

The NTSB determined that the probable cause of the accident was the pilot's loss of airplane control during a known one-engine-inoperative condition. The reasons for the loss of control and engine shutdown couldn't be determined because the airplane wasn't equipped with a crash-resistant recorder, and post-accident examination and testing didn't reveal evidence of any malfunction that would have precluded normal operation.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, visit www.ntsbreporter.us or write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.

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