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Iced Up

posted Apr 17, 2011, 2:38 PM by George Finlay   [ updated Sep 16, 2015, 7:10 AM by Nathaniel Cauldwell ]

About 1900Z on Saturday December 6, 2008, the pilot of Cessna 206 N6053B about 10 miles north of Traverse City requested a clearance for the ILS 28 instrument approach to land at Cherry Capital Airport (KTVC). The approach plate is provided in the links section at the end of this article.

His communications with Minneapolis Center make it clear he had encountered structural ice. The pilot was not able to land after flying the approach, lost communication contact with ATC, then lost control. The airplane was destroyed and the pilot killed when he struck a mobile home east of the airport.

He had departed South St. Paul MN Municipal Airport (KSGS) about 1615Z on an IFR clearance, cruising at 11,000 feet, headed home to Glens Falls, NY (KGFL), a distance of about 870 nautical miles. He had left a voicemail for Dick Bovey, his instructor in Glens Falls, in which he said he had received a weather briefing that led him to believe he would be able to fly above a storm then over the Great Lakes. We assume he meant he talked with a Lockheed Martin briefer, but we do not know at what time. Those briefings are recorded, but not available to the general public. There was an AIRMET ZULU for moderate icing below 16,000 feet over Wisconsin and Michigan along his route, issued at 1445Z by Chicago, and expected to continue beyond 2100Z thru 0300Z. Since he departed about 1615Z, he may have received his briefing before 1445Z when an earlier AIRMET ZULU issued by Chicago at 0845Z, valid at 1500Z and expected to continue through 2100Z, limited the icing forecast to altitudes below 12,000 feet.

A detailed study of weather conditions at the time of the accident by meteorologist and CFI Scott Dennstaedt will be available soon at AvWxWorkshops.com. In it, Scott concludes that the flight encountered lake effect icing conditions over Lake Michigan. For more information, contact Mr. Dennstaedt at Scott@chesavtraining.com, or (803) 802-2591.

The newly-minted instrument pilot, Keith Harris, alone in the plane, reported structural ice to Minneapolis Center and said he was turning around and heading back west. That might have been a better plan, with Green Bay, 100 miles to the west, reporting VFR conditions, while Traverse City was low IMC with one mile visibility in snow at the time he reported an increasing ice accumulation to Minneapolis Center. He rejected that plan, and accepted vectors to the approach, possibly because he had already accumulated ice along his route to the west. The radar track shows him climbing to 14,500 shortly before he requested the approach into Traverse City, probably in an unsuccessful effort to climb out of ice.

N6053B was not approved for flight in known ice (FIKI), and had only the usual limited anti-ice provisions in such non-FIKI aircraft. There was pitot heat, which helps prevent the pitot tube from becoming clogged with ice. A clogged pitot tube causes erroneous airspeed indication in the cockpit which can make it difficult for the pilot to maintain control. There was an alternate static source in the cockpit that would continue to provide accurate static air pressure in the event the two outside pressure sources became clogged by ice. If ice interfered, the reliability of the altimeter, vertical speed indicator, and airspeed indicator would be compromised. Both of those remedies would require that the pilot remember to use them. Given his inexperience and the effect of stress on his thinking, he may not have. One item of automatic ice protection on his airplane is a spring-loaded door in the air intake plenum that is designed to open if the filter covering the normal induction air intake becomes blocked by ice.

He reports that his windscreen is iced over. He did have a defrost control that would redirect cabin heat toward the bottom inside of the windscreen. But it is not designed to clear structural ice from the outside of the windscreen. The amphibious floats on the airplane made it less able to deal with an accidental icing encounter like this by provided additional surfaces on which ice could collect.

His communication with Minneapolis Center as he is vectored to the approach made it apparent he had a glideslope, but no localizer indication, even though both signals was being broadcast normally. There is a link below to these communications, edited to remove silences and communications with other aircraft. Ice may have already been building up to a level where it was beginning to interfer with the “whisker antenna” on the vertical stabilizer that is responsible for receiving those signals.

Shortly after he missed the approach, the air traffic controllers lost communication with him. It is possible that ice caused both of the COMM/GPS antennae to break off. Without help from controllers, and without a GPS signal, his best tactic would have been to use the compass and autopilot to fly away from the icy clouds being generated over the lake. But it is difficult, even for an experienced pilot, to continue to think clearly in dire situations, and he did not take that course. Equipped with floats, he may have been considering a water landing, though that would have been difficult in the strong winds and low visibility reported at the time, even if he had been able to locate the lake. At the time of the accident, there was a wind at the airport of 13 knots gusting to 26, with 0.5 miles visibility and vertical visibility of 500 feet in snow.

The radar track shows him flying around in circles about 15 miles east of the airport at low airspeeds for some time before he impacted trees and then the mobile home about 2015Z.

When he purchased this airplane in 2006, I provided Keith an introduction to the 206 and the Garmin G1000 avionics suite. In February 2007, I gave Keith and his instructor and designated examiner Dike Bovey additional familiarization training with the G1000 and the King KAP140 autopilot. Keith earned his instrument rating in February 2008.

Thanks to Doug Robertson and Airport-data.com for the use of the photograph of 6053B moored on Lake George this past summer. Thanks to Live-ATC.com for the audio, and to FlightAware.com for the radar data.

I offer Keith’s wife and family my heartfelt sympathy for their loss.

Links:

N6053B moored on Lake George, summer 2008

AvWxWorkshops.com

N6053B flight track

ILS28 at KTVC

ATC/Harris communications part 1

ATC/Harris communications part 2

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