1993 — April 19, Plane Crash kills SD Governor Mickelson & party, near Zwingle, IA– 8

–8  AP. “Plane crash altered state’s political scene.” Huron Plainsman, SD, 12-30-1993, p. 12.

–8  Associated Press. “State mourns Mickelson.” Huron Plainsman, SD, 4-20-1993, p. 1.

–8  NTSB. Aircraft Accident Report. In-Flight Loss of Propeller Blade…, “Executive Summary”

 

Narrative Information

 

April 20: “Dubuque, Iowa (AP) — A small jet carrying South Dakota Gov. George Mickelson crashed in heavy rain on a farm near Dubuque, killing all eight aboard. The plane sheared off a farm silo and crashed through a barn, starting a fire that destroyed the building….

 

“The twin -engine turboprop had been headed for an emergency landing at the Dubuque airport when it struck the barn and silo about 14 miles southwest of Dubuque about 4 p.m. Monday, said Sandra Campbell, a spokeswoman at the Federal Aviation Administration regional office at Kansas City, Mo. ‘The pilot reported a lost engine and lost pressurization. The aircraft then was handed off to the Dubuque tower for clearance to land. It was the nearest location,’ Mrs. Campbell said. ‘It was cleared to land. About a minute after the last transmission, the Dubuque tower reported to the sheriff the aircraft was down on the ground,’ she said.

 

“The other victims were: South Dakota Economic Development Commissioner Roland Dolly, state energy Policy Commissioner Ron Reed, Sioux Falls [SD] banker Dave Birkeland, Roger Hainje, director of the Sioux Falls Development Foundation, Angus Anson of Northern States Power in Sioux Falls and two pilots from Pierre, S.D., Ron Becker and Dave Hansen.

 

“The plane was returning from Cincinnati, Ohio, where the governor met with officials of John Morrell and Co., said Janelle Toman, Gov. Mickelson’s press secretary. Officials of the state and the city of Sioux Falls had been concerned about the future of a plant in Sioux Falls, Toman said….

 

“Michelson, 52, a Republican, was elected governor of South Dakota in 1986, defeating Democrat R. Lars Herseth, a state representative. He was re-elected in 1990, defeating Democrat Bob Samuelson. Before becoming governor, Mickelson served six years in the South Dakota House, where he was speaker in 1879-80….

 

“Lt. Gov. Walter Dale Miller will be sworn in as South Dakota’s 28^th governor this afternoon, said governor’s spokesman Tony Mangan….” (Associated Press. “State mourns Mickelson.” Huron Plainsman, SD, 4-20-1993, p. 1.)

 

NTSB Executive Summary: “On April 19, 1993, at 1552 central daylight time, a Mitsubishi MU-2B-60, registered in the United States as N86SD and operated by the South Dakota Department of Transportation, as a public use airplane, collided with a silo on a farm near Zwingle, Iowa, while attempting an approach to an emergency landing at Dubuque Regional Airport, Dubuque, Iowa. The airplane was destroyed in the collision and postcrash fire. The captain, first officer, and the six passengers aboard were fatally injured. Instrument meteorological conditions existed at the time. The flight originated from Cincinnati, Ohio, at 1406, on an instrument flight rules flight plan.

 

“The National Transportation Safety Board determines that the probable cause of this accident was the fatigue cracking and fracture of the propeller hub arm. The resultant separation of the hum arm and the propeller blade damaged the engine, nacelle, wing, and fuselage, thereby causing significant degradation to aircraft performance and control that made a successful landing problematic.

 

“The cause of the propeller hub arm fracture was a reduction in the fatigue strength of the material because of manufacturing and time-related factors (decarburization, residual stress, corrosion, mixed microstructure, and machining/scoring marks) that reduced the fatigue resistance of the material, probably combined with exposure to higher-than-normal cyclic loads during operation of the propeller at a critical vibration frequency (reactionless mode), which was not appropriately considered during the airplane/propeller certification process.

 

“The safety issues in this report include the propeller hub design, certification and continuing airworthiness, and air traffic control training. Safety recommendations concerning these issues were addressed to the Federal Aviation Administration.” [p. vi.]

 

“….At 1540, the flightcrew reported, ‘Chicago, sierra delta, we had a decompression,’[1] then ‘Mayday, Mayday, Mayday. Six sierra delta, we’re going down here.’ The Chicago Air Route Traffic Control Center (ARTCC) controller acknowledged: ‘Roger, tell me what you need.’ The flightcrew replied. ‘The closest airport we can get to here.’ The controller informed N86SD that DBQ was 25 miles away at their 2:00 position and asked what altitude the airplane needed. The airplane’s position was actually 37 miles from DBQ. At this time, the controller was unaware of the weather at DBQ. The flightcrew responded, ‘We need to get down to our oxygen level.’ The center controller then cleared the airplane to 8,000 feet.” [p. 2.]

 

“About this time, other airports were considered as divert options. The controller later stated that there were smaller airports in the area but that they were uncontrolled and unmanned. She considered Maquoketa Airport, but it only had a nondirectional radio beacon (NDB) instrument approach. She considered Quad City Airport (MLI), Moline, Illinois, but believed it was farther away from the airplane than DBQ.

 

“At 1542:12….DBQ was about 31 miles from the airplane. Also at that time, the current weather observation for MLI (about 33 miles away from N86SD) indicated visual meteorological conditions (BMC) on the surface. Also at that time, instrument landing system (ILS)-equipped Clinton Airport (CWI), Clinton, Iowa, was 9 miles south, with a ceiling of 400 feet, and a visibility of 5 miles. The air traffic controllers involved in the emergency situation did not query their computer for the MLI surface observation, which would have been available….

 

“At 1544, the controller asked, ‘Can you hold altitude?’ The flightcrew responded, ‘Well, standby.’ The controller then cleared the flight to 6,000 feet. At 1545, the airplane reported difficulty holding altitude, and the controller then cleared the flight to 4,000 feet and restated the heading to join the approach course. [p. 4.]

 

“….On April 28, 1993, the FAA issued AD 93-09-04 concerning Hartzell Model HC-B4TN-5 propellers installed on MU-2B-60 airplanes. The purpose of the AD was ‘to prevent fatigue cracks in propeller hub arm assemblies progressing to failure, resulting in departure of the hub arm and blade, and that may result in engine separation and subsequent loss of aircraft control….’ It required that the propeller hubs on all MU-2B-60 airplanes be magnetic particle inspected with the pilot tubes removed. The AD required that the inspection be repeated at 600-hour intervals.

 

“On June 10, 1993, the FAA issued AD 93-12-01. This AD extended the provisions of AD 93-09-04 to Hartzell model HC-B4TN-5 propellers installed on other MU-2B airplanes….” [p. 43.]

 

“The air traffic control sector in which the decompression occurred was called to Coton High sector. This sector controls airplanes at and above flight level 240. Small airports are not normally depicted on the radar map used for high sectors. However, the controller working the sector (manual) position reported that to assist the radar controller, she depressed the sector boundary button to bring up additional airports that are not normally displayed on the radar screen. CWI was then displayed, as well as DBQ and MLI. Additional information can be obtained on a specific airport by the controller by typing the letters ‘A’ (meaning ‘airport information’) into the computer, then placing the cursor over the airport symbol on the screen and pressing the ‘enter’ key. Information such as airport elevation, UNICOM frequency, pilot-controlled lighting capability, runway surface, longest runway, nearest navigation aid and primary navigation aid, appear on a small display adjacent to the radar screen. This additional available information was not brought up by the controller involved in this airborne emergency.” [pp. 47-48.]

 

“….Pilot Decisions on Flying the Airplane. The Safety Board examined the appropriateness of the pilots’ decisions. The Board noted that the pilots initiated an emergency descent and descended down to and through 9,000 feet in a very rapid manner very likely because of the cabin depressurization. Had they attempted to arrest the descent at 12,000 feet, for example, and turned toward DBQ at the first instruction for a northerly turn from ATC, they might have had sufficient range to reach DBQ. In addition, had the crew stated the true seriousness of their situation to Coton High controllers, the controllers might have been more prone to search for a more suitable diversion airport….” [p. 62]

 

“The Safety Board concludes that the pilot acted in a reasonable manner in continuing the high rate of descent to lower altitudes and that once he was at lower altitudes, he continued to fly at higher airspeeds and rates of descent to gain more aerodynamic control.” [p. 63.]

 

“Air Traffic Control Actions. Following the loss of the propeller blade and the decompression, the flightcrew requested from the Chicago ARTCC controller vectors to the ‘closest airport we can get to…,’ at 15440:46. Four seconds later, the controller transmitted that DBQ was at the airplane’s 2:00 position and 25 miles away. DBQ was actually about 37 miles from the airplane.[2] At that time, the airplane was within 2 miles of being equidistant from MLI and DBQ and only about 9 miles from CWI. The DBQ and CWI local areas were experiencing IFR [Instrument flight Rules] weather conditions, and the MLI local area was experiencing VFR [Visual] weather conditions….

 

“The Safety Board believes that N86SD would have broken out of the overcast at a higher altitude if it was on a course toward MLI rather than DBQ, although N86SD was not offered this option by the controllers. This would have given the pilot more time to select a flat, open area on the ground to crash land the airplane, and the probability of flightcrew and occupant survival would have been greatly increased.” [p. 63.]

 

“….The Safety Board believes…that the controllers involved in this emergency should have, at some point, determined that the weather at MLI was much better than that at DBQ. Moreover, they should have been aware that SWI was much closer than either MLI or DBQ and then relayed that information to the pilots of N86SD. The air traffic control transcript revealed that an apparent lull in controller activity occurred shortly after N86SD was given the DBQ weather. This would have been a good opportunity for the controllers to identify other possible diversion airports, obtain weather sequences for one or more of these airports, and then transmit some options to the pilots of N86SD. As it happened, of the several airports in the area with instrument approach capability and weather above instrument approach minimums, the pilots were given information on only one airport, DBQ.” [p. 64.]

 

“Once a flight declares an emergency, the role of air traffic control reverts from one of controlling the flight to one of assisting the flight in safe recovery. Ideally, an exchange of information between the flightcrew and the controllers should have taken place to allow the safest resolution of the emergency situation. The controllers should not have hesitated to pass any potentially helpful information to the flightcrew, however sketchy that information might have been, thereby offering them the maximum number of options.

 

“There were also systemic shortfalls that hindered the effectiveness of the assistance that the controllers could provide N86SD. These include a lack of readily available current weather sequence reports for the controllers, and a lack of written guidance for controllers during emergency situations.” [p. 65.]

 

Conclusions…Findings

 

“….13. There was no routine of special inspection in place at the time of the accident that were designed to detect the fatigue crack that precipitated the loss of the propeller blade. Subsequent to the accident, efforts to develop a practical, nondestructive test, without the removal of the pilot tubes to detect such an anomaly, were unsuccessful.” [p. 69.]

 

(NTSB. Aircraft Accident Report. In-Flight Loss of Propeller Blade and Uncontrolled Collision with Terrain, Mitsubishi MU-2B-60, N86SD, Zwingle, Iowa, April 19, 1993. 11-16-1993.)

 

Sources

 

Associated Press. “Plane crash altered state’s political scene.” Huron Plainsman, SD, 12-30-1993, p. 12. Accessed 12-15-2018 at: https://newspaperarchive.com/huron-plainsman-dec-30-1993-p-12/

 

Associated Press. “State mourns Mickelson.” Huron Plainsman, SD, 4-20-1993, p. 1. Accessed 12-16-2018 at: https://newspaperarchive.com/huron-plainsman-apr-20-1993-p-1/

 

National Transportation Safety Board. Aircraft Accident Report. In-Flight Loss of Propeller Blade and Uncontrolled Collision with Terrain, Mitsubishi MU-2B-60, N86SD, Zwingle, Iowa, April 19, 1993. Washington, DC: NTSB/AAR-93/08, adopted 11-16-1993, 131 pages. Accessed 12-16-2018 at: https://www.ntsb.gov/investigations/AccidentReports/Pages/AAR9308.aspx

 

[1] At page 68, Conclusion 4, the NTSB speculates that as part of the sequence of events initiated when the propeller hub arm on the left propeller failed, “One or more of the remaining propeller blades, and/or a released blade tip from one of the remaining propeller blades, might have contacted the fuselage, causing a cabin decompression.”

[2] Air traffic control personnel stated that the inaccuracy of the radar presentation (at the radar range setting customarily used) accounted for this 12-mile error.