Probable Cause #28: Scud Run Gone Bad

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This article originally appeared in Aviation Safety, Jan. 2005.

Probable Cause

Scud running is the time-honored practice of trying to stay VFR down low between weather and terrain while motoring off to a destination. Generally, it involves a VFR-only pilot flying in good daytime visibility over flat terrain at an altitude that will clear charted obstacles. While this kind of operation can be performed safely, it definitely poses higher risks than, say, cruising to the beach on a CAVU summer day. When flying at low level, at night and in reduced visibility over unknown territory and at a high speed, bad things can happen quickly. Too quickly.

When contemplating this kind of flight, it must be approached with a healthy respect for terrain, obstacles and visibility limitations. Planning a route to avoid the highest terrain, constantly updating the location of an airport to duck into and maintaining a forward speed that allows plenty of time to see, recognize and avoid obstacles are all keys to making a scud-running operation work well.

Ensuring adequate visibility cannot be overstressed, since the faster you fly when scud running, the less time you have to visually acquire terrain and obstacles and then maneuver to avoid them. At night, scud running at any speed is a really bad idea for exactly this reason.

Background

Cirrus SR22

On January 18, 2003, at 0638 Central time, a Cirrus SR22 was destroyed following an in-flight collision with terrain near Hill City, Minn. The Private pilot and single passenger were fatally injured. The airplane had departed the Grand Rapids/Itasca County Airport (GPZ) in Grand Rapids, Minn., at 0630, with an intended destination of the St. Cloud (Minn.) Regional Airport (STC). Marginal VMC or IFR conditions prevailed in the area of the two airports and at the accident site. An AIRMET calling for occasional ceilings below 1000 feet agl and/or visibilities below 3 statute miles in light snow showers and blowing snow was in effect at the time of the accident as was another AIRMET for occasional moderate turbulence below 8000 feet msl. The IFR conditions along the route from GPZ to STC were expected to continue beyond 0900, ending around 1200.

On the morning of the accident, civil twilight began at 0720 in Grand Rapids, Minn., with sunrise at 0754. There was a full moon earlier in the morning, at 0448. The pilot received two weather briefings from the Princeton (Minn.) Automated Flight Service Station on the morning of the accident. Both briefings noted the marginal VFR weather and AIRMETs in effect for the flight.

The airplane was a 2002-model Cirrus SR22, less than two months old. Total time on the airframe and engine at the time of the accident was 35.7 hours. Its pilot, age 47, held a Private pilot certificate and, according to a logbook found in the wreckage, had logged 248.0 hours total time. Of these, 18.9 were in an SR22. Except for 1.0 hour in a simulator, the remaining flights logged were in a Cessna 172.

The pilot had 57.0 hours of instrument time and 19.0 hours of night. Instrument and night flight time in the SR22 totaled 0.3 and 2.3 hours, respectively. According to Cirrus Design/University of North Dakota records, the pilot completed the SR22 training course on December 12, 2002. The course involved 12.5 hours of dual flight instruction and 5.3 hours of ground instruction. A VFR-only completion certificate and High Performance aircraft endorsement limited to SR22 were awarded the pilot on December 12, 2002.

Witness Reports

Several witnesses reported seeing and/or hearing the aircraft shortly before the accident. One witness stated the aircraft appeared to be following a nearby road at an altitude estimated as 100 feet above the trees. He noted the engine sound was smooth; it "wasn't laboring." Another witness noted the engine seemed to be at full throttle and that it "wasn't missing." A third witness, located about 1/2-mile south of the accident site, heard the aircraft fly over. He stated that it "sounded like the prop wasn't catching any air. It was just screaming." Approximately 3-4 seconds after the aircraft flew over, he stated that he heard what he considered to be the impact. He noted that as he was looking out his window, he saw a "fireball" up over the trees. He recalled the weather conditions at his location as clear, with a full moon.

Investigation

Scud running

The aircraft impacted into level wooded terrain. The entire debris path was approximately 500 feet long, oriented on a 280-degree magnetic heading. Despite the airframe's fragmentation, all major components were found in the debris field. Portions of the cabin and several wing skin fragments, as well as localized ground cover and trees within the debris area, exhibited evidence of a post-impact fire.

Radar data obtained from the FAA's Minneapolis Air Route Traffic Control Center indicated a single VFR transponder code in the vicinity of GPZ about the time of the accident. The initial radar contact was at 0630:16 over GPZ at 1700 feet pressure altitude. The aircraft associated with the beacon code proceeded southbound, paralleling Minnesota Highway 169, and reached a maximum of 3200 feet pressure altitude. At 0636:51, the target began a descending left turn, reaching a pressure altitude of 2400 feet at 0637:27. This was an average descent rate of 1166 fpm. At this point, the target entered a climb with a decreasing-radius left turn.

The final radar contact, at 0637:39, was plotted to be 0.21 nautical miles from the accident site. The aircraft's Mode C transponder data displayed 2900 feet pressure altitude. This evidence suggests an average climb rate of 2500 fpm from a pressure altitude of 2400 feet at 0637:27.

The aircraft's average ground speed, true airspeed and climb/descent rate were computed based on the raw radar data and measured winds aloft. The aircraft's true airspeed averaged 191 knots over the final one minute of radar data. The rate of climb averaged 2500 fpm between the final two radar data points. This followed an average descent rate of 2000 fpm, 36 seconds earlier, between 0636:51 and 0637:03.

According to the NTSB, the Cirrus Design SR22 Pilot's Operating Handbook (POH) specifies a never exceed speed, Vne, of 204 knots calibrated airspeed. This airspeed is represented on the airspeed indicator as a red radial line. The aircraft's maximum structural cruising speed, Vno, represented as the top of the green airspeed arc, is denoted as 180 knots. The POH also lists a rate of climb of 1428 fpm at sea level and -20 C ambient temperature.

Conclusions

The factors present in this accident go beyond the classic "scud-running" scenario. In addition to disregarding the dangers of night operations in poor weather, the pilot was inexperienced in his brand-new aircraft; he had little time in it at night and almost no instrument work. The decision to launch in marginal nighttime conditions -- even though witnesses reported a clear sky -- is an unmistakable sign of overconfidence, perhaps in the well-equipped airplane, perhaps in the pilot's skills -- perhaps in both.

While there is no way to know what pressure, if any, the pilot felt he was under to complete the flight, waiting for daylight might have made the difference. Slowing down might have, also. The bottom line, however, is that an Instrument-rated pilot would have been able to climb through the low clouds and avoid hitting the terrain.


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