An all-too-common accident in turbine single-pilot minimums approaches
Over the years we've seen a relatively large number of approach accidents involving aerodynamic stalls during the last moments of instrument approaches. The airplanes involved — often turboprops — are typically flown by experienced, professionally qualified pilots who somehow get behind the situation as they transition from instruments to visual reference. More often than not, the operation is single pilot.
This month, we'll look at the investigation into the loss of Mitsubishi MU-2B-60 N80HH. The pilot and three passengers were killed when the aircraft crashed during an instrument approach to Runway 07 at Lorain County Regional Airport (LPR) in Elyria, Ohio. This accident is in no way extraordinary, and that is what makes it worth reviewing, I think. Perhaps in examining the investigator's findings, you'll come away with the sense that the last moments of an instrument approach are always the most critical.
The surface weather observation at LPR at 1353 on Jan. 18, 2010, indicated the following conditions: winds, 240 deg. at 9 kt.; visibility, 2 mi. in mist; overcast at 500 ft.; temperature, -1C; dew point, -3C; altimeter, 29.93. Weather Depiction Charts for 1100 and 1400 depicted an extensive area of IFR conditions over the region. The closest VFR conditions were over 200 mi. south of Elyria. The freezing level was at the surface with freezing temperatures at all levels aloft.
Pilots reported an extensive overcast layer extending over Ohio with bases from 100 to 1,200 ft. and tops at 2,200 to 3,800 ft. There were 12 reports of light rime to mixed type icing, and four reports of light to moderate intensity icing conditions in clouds below 3,000 ft.
The accident flight departed Gainesville (Fla.) Regional Airport at 1100 on an IFR flight plan. The 30-year-old ATP-rated pilot was in the left seat and was conducting the flight as a single-pilot operation. A private-pilot-rated passenger occupied the right seat, and two passengers were seated in the cabin. This was an FAR Part 91 operation. The en route flight phase was without incident. Investigators used ATC recordings, radar track analysis and eyewitness testimony to put together the details of the approach phase.
The airplane approached LPR on a heading of 325 deg. At 1335:51, ATC informed the pilot that he could expect radar vectors for the ILS Runway 7 approach. Runway 7 is 5,002 ft. long; airport elevation is 794 ft. The ILS Runway 7 approach course is 070 deg.; glideslope/glidepath intercept altitude is 2,400 ft.; straight-in landing minimums were 994 ft. MSL DH with one-half mile visibility. Circling approach minimums were 1,240 ft. MSL MDA with 1-mi. visibility.
At 1345:53, ATC informed the pilot that he was 4.5 miles from RAWLS, the final approach fix for the approach, and instructed him to turn right to a heading of 050 deg. and maintain 2,600 ft. until established on the localizer. The flight was cleared for the ILS Runway 07 approach. The pilot acknowledged the clearance. Radar track data indicated that the airplane flew through the inbound course of 070 deg. and continued on a 055-deg. heading.
At 1347:03, ATC instructed the pilot to turn to 090 deg. to intercept the inbound course. The ATC controller also stated, “I didn't adjust for the wind there.”
At 1347:19, ATC instructed the pilot to turn to 100 deg. and asked the pilot if he wanted to continue the approach or accept radar vectors to get reestablished on the inbound course, since he would be intercepting the inbound course near or at RAWLS. The pilot elected to continue the approach.
At 1348:27, ATC instructed the pilot to change radio frequency to LPR's advisory frequency. The pilot acknowledged the frequency change.
At 1349:33, the pilot advised ATC that he was executing a missed approach. Radar track data indicated that the airplane's altitude during the approach was never lower than 1,500 ft. MSL. The decision height for the ILS Runway 7 approach was 994 ft. MSL.
At 1350:29, ATC instructed the pilot to climb to 2,500 ft. MSL and turn left to a heading of 280 deg. for radar vectors for the ILS Runway 07 final approach course. The pilot requested that the controller extend the outbound leg to provide more time to get established on the inbound course. The radar track data indicated that the airplane was about 11 mi. from the airport before it turned inbound to intercept the inbound localizer course.
At 1358:18, ATC instructed the pilot to turn left to 100 deg. and maintain 2,600 ft. MSL until established on the localizer. The flight was cleared for the ILS Runway 7 approach. The pilot acknowledged the clearance.
At 1401:12, ATC instructed the pilot to change to the advisory frequency. The pilot acknowledged the frequency change. Radar track data indicated that the airplane's altitude increased to about 3,000 ft. MSL when it turned inbound and intercepted the localizer. The altitude was about 2,200 ft. MSL when it crossed RAWLS. (The crossing altitude at RAWLS is depicted as 2,263 ft. MSL).
The airplane continued inbound and the altitude continued to decrease. The radar track data indicated that the airplane had descended to 1,300 ft. (506 ft. AGL) about 1 mi. from the runway. The airplane's heading had started to go left of the centerline when it was at about 1,400 ft. MSL, and it continued to drift left until the last radar return. The last radar return indicated that the airplane was about 1,000 ft. left of the centerline and 206 ft. AGL. The linear distance from the last recorded radar return to the initial impact point was about 750 ft.
A witness — waiting at the airport for the airplane to arrive — heard the Unicom transmissions and looked toward the approach end of the runway to watch the arrival. He spotted the airplane as it descended out of the clouds. It was in a nose-low attitude, rolling to the right into a steep right turn with the wings at almost a 90-deg. position relative to the ground. The airplane was “definitely out of control” when he saw it.
The witness saw a “huge cloud of snow” billow up as the airplane struck the ground. When the snow cloud cleared, he observed the airplane wreckage at the west end of the airport property. It all happened very fast, he told investigators — “in the blink of an eye.” He reported that the airplane's landing light was off as it descended.
Another witness told investigators he heard the airplane as it was approaching his house near the airport. He looked out a window and saw the airplane about 150 ft. above the ground. Using an airplane model to describe the airplane's flight profile, he indicated that he observed the airplane in a 60-deg., nose-low attitude with an 80-deg. right bank.
The airplane had impacted a field within the airport's boundary about 2,150 ft. west of the Runway 07 threshold and about 720 ft. north of the extended centerline of Runway 07. The wreckage path was 194 ft. long and was oriented on a heading of 100 deg. magnetic. The wings and landing gear separated from the fuselage. The cockpit cabin had partially separated from the rest of the fuselage during the impact sequence, but the flight control cables were not severed. The empennage remained attached to the fuselage. There was no post-impact fire.
The pilot and passengers were dead on the scene of multiple blunt force trauma. There was no indication of pre-impact physical impairments and the's Civil Aeromedical Institute tests were negative for the list of drugs and pharmaceuticals normally checked.
Inspection of the wreckage revealed that the landing gear had been extended and the flaps were set to 5 deg. The pitch trim indicator was about 15 deg. nose-up, the rudder trim indicator was about 1-2 deg. right, and the aileron trim was neutral. The trim surfaces corresponded to the indicated trim settings.
The flight control cables were examined for continuity. The elevator and rudder push-pull rods and cables exhibited continuity from the flight controls to the control surfaces. The wing spoiler cables had continuity from the control yoke to the mixer box located in the wing center section. The push-pull tubes from the mixer box to the spoilers were broken and exhibited impact damage. The attach points of the push-pull tubes to the spoiler bell cranks exhibited continuity.
The airplane's twoTPE331-10-511M turboprop engines were disassembled and examined at the factory. Both exhibited rotational scoring of the first-stage compressor impeller shroud. The leading edges of the first-stage impeller blades were bent opposite the direction of rotation. There was rotational scoring through 360 deg. on the second-stage compressor housing impeller shroud and rotational scoring on the shroud line of all second-stage compressor impeller blades. The engines also exhibited metal spray deposits adhering to the suction side of the second-stage turbine stator vanes and to the suction side of the second-stage turbine blades. Both had rotational scoring damage to the sun gear and propeller shaft. In other words, they were operating at impact. The propellers and gearboxes showed no pre-impact damage. Special studies of the autopilot turned up no pre-impact studies.