Safety Pilot: Landmark Accidents: Three strikes

In baseball, it’s three strikes and you’re out. In aviation, after a critical foul-up you might get another chance. It’s unusual, however, for a pilot to destroy one aircraft—and badly damage a second one—before learning that the same ill-advised act might not be life-prolonging.

Thunderstorms are dangerous. This is preached early to every pilot. Bigger questions are what, if anything, should be done to prevent mishaps like this—and is that possible?

The flight and weather. On October 26, 2010, the pilot called Flight Service about 9 a.m. to file an IFR flight plan for a 9:20 a.m. departure from Olive Branch, Mississippi (OLV) for Dekalb-Peachtree Airport (PDK) in Atlanta, Georgia. The aircraft was a turbocharged Beechcraft Bonanza A36TC. The planned cruise altitude was 17,000 feet with an estimated time en route of one hour and 35 minutes.

The briefer asked, “Do you require the latest adverse [weather] conditions?” The pilot replied, “No, that’s why we are getting out of here.” At the end of the call the briefer confirmed, “You did say you had the adverse conditions?” The pilot replied, “Yes, I do.”

The day was expected to be stormy. The National Weather Service (NWS) predicted that from 4 a.m. until noon severe thunderstorms could be expected with hail, wind gusts to 70 knots, and extreme turbulence, with maximum cumulonimbus tops to 45,000 feet, moving at 50 knots. By the time the Bonanza was airborne, at about 9:25 a.m., two convective sigmets had been issued for a line of embedded thunderstorms that lay across the proposed flight path and moving eastward at 35 knots.

According to the NTSB report, “A review of recorded radar track information and radar precipitation information provided to the controller…the aircraft’s flight path approached and entered an area depicted as heavy to extreme precipitation.” The Bonanza was level at 15,000 and had been cleared to FL210.

The controller provided a pilot report from a Cirrus that had passed through the area about 20 minutes earlier. The Cirrus pilot reported light turbulence and heavy rain for about a minute. It had flown through a gap in the line “that was yellow to green on our onboard radar, versus red on either side of it. It was fairly good.” The Cirrus was 5,000 feet lower and several miles north of the point where the Bonanza entered the area of heavy precipitation. The controller offered no additional information regarding the weather that was depicted on his scope but allowed the pilot to deviate as needed, and the pilot requested no weather information or vectors.

At 9:54 a.m. the Bonanza was on an easterly track at 14,800 feet. According to the NTSB, “The last three radar targets (each 10 seconds apart) displayed altitudes of 14,800, 14,700, and 13,900, where radar contact was lost. Interpolation of the last two radar targets suggested a 4,800-feet-per-minute rate of descent. At the time the radar target was lost, the airplane was in an area of depicted extreme-intensity precipitation.” The results were fatal to the pilot and passenger.

Wreckage. Details of the wreckage usually are not relevant to our discussion, but in this case there’s some educational value in portraying the violence of a severe thunderstorm—something the accident pilot apparently did not appreciate. The Bonanza wreckage was scattered over an area approximately 15 miles in length.

From the NTSB: “About 70 percent of the airplane was recovered, and parts associated with the nose, tail, and both wing tips of the airplane were identified. Parts not located were the right aileron, vertical stabilizer, rudder, horizontal stabilizers, left elevator, and the outboard portion of the right elevator. The wreckage was fragmented into large and small pieces. All fractures and failures were consistent with overload failure induced by air load or impact. All control cable, chain, bell crank, and pulley failures were consistent with overload. The forward spar carry-through upper cap was fractured and separated approximately 20 inches from the left wing. The spar web contained diagonal compression buckles and was twisted and bent forward at the right wing carry-through. The right wing leading edge contained diagonal compression buckling in the upward direction. The aft cabin floor contained clockwise torsional buckling. The fuselage structure was not attached to the aft cabin floor and skin tearing signatures were visible on both lower longitudinal skin lap joints (left and right side) throughout its length.” To put this a bit more succinctly—the aircraft was shredded.

Pilot. The pilot held a private certificate with an instrument rating, 790 total hours of flight experience, and 59 hours in actual instrument meteorological conditions. The pilot had flown 40 hours in the preceding 90 days.

Aircraft. The 1992 Turbo Bonanza had a total of 2,275 airframe hours at the time of the last annual inspection in August 2010. It was equipped with dual Garmin 430W units and a satellite weather service subscription. It’s reasonable to assume that the pilot probably was viewing datalinked Nexrad radar, although that is not confirmed. Data retrieved from the engine instruments and from teardown after the accident indicated no powerplant malfunction.

From the NTSB: “According to a maintenance/repair receipt dated July 14, 2007, airframe repairs due to stress were completed on the accident airplane. Some of the parts replaced included left- and right-hand stabilizer assemblies, left- and right-hand wing skins, as well as belly skin. According to the owner/operator of the repair facility, this was the second airplane that the pilot/owner had brought to him for repair after flying through heavy weather. The second airplane was brought to the facility within 30 days of the first.”

The pilot had brought another Bonanza A36 to the same shop a month earlier, which was “totaled.” When the pilot showed up he announced, “I did it again.” The shop owner stated, “In my 33 years of aviation I learned [that] when these things happen [the accident], we knew it would happen in advance. I worried about [the pilot] for two years. He was doing better and I started to quit worrying.”

Analysis. The NTSB had not completed the probable cause finding at this writing, but here are my observations.

A thunderstorm forecast doesn’t necessarily mean that the day will not be flyable, but the context of the weather system is important. Early mornings with high temperatures and dew points mean plenty of energy to kick things off; once the convection process starts, things can get ugly in a hurry.

Higher altitudes are sometimes better because the buildups may be more easily seen, but the mid-teens and above can be terrible unless you are able to get above the veiling clouds. Until a flight can top a CB by several thousand feet, which may mean getting to FL400 or higher, lower is sometimes the better choice.

Early airline pilots in DC–3s used to slip below and between cells as low as possible. This tactic doesn’t always work and should be considered only if one is boxed in. An off-airport landing may be a better choice—the aircraft may be damaged, but the survival rate for passengers and pilots is much better. A far superior option is to make a one-eighty before getting into dire straits.

Convective sigmets demand attention because now the forecast has become reality. Pay close attention to the speed of the cells—fast-moving (generally above 15 to 20 knots) indicates a powerful system. Slow movement, however, does not indicate safety.

Pireps in convective weather must be accepted with great skepticism. The Cirrus pilot misstated that he had onboard radar (it was datalinked Nexrad), and he did not state how far away he was from the red areas. With severe storms, a 40-mile gap is recommended. If he was in heavy rain my guess is he was a bit too close. A 20-minute-old report from a different altitude can easily lead one astray. Strong cells can grow more than 4,000 feet per minute, and a 20,000-foot “bouncer” can go to a 30,000-foot killer in just a few minutes. Don’t forget that they generate laterally as well.

During the accident debrief, the controller indicated that he didn’t trust the weather display on his scope and felt that pilots were often far better able to see the weather. He did relay the pirep but didn’t warn the pilot of the heavy extreme returns on the scope. This is contrary to the guidance provided in the controller’s handbook, which requires an advisory to pilots of any depicted moderate or greater precipitation.

Experienced controllers are masterful in moving traffic through convective areas, but you have to ask for vectors. ATC radar and our in-cockpit displays only show precipitation, which doesn’t necessarily correlate to turbulence. If there’s the least bit of uncertainty about where the cells are after discussion with ATC, a completely different plan is needed, and that’s your call as PIC. Review the Air Safety Institute’s two online courses, Weather Wise: Thunderstorms and ATC and IFR Insights: Cockpit Weather to understand ATC’s role, as well as the limitations of both ground and airborne equipment.

The overwhelming responsibility for this mishap resides with the PIC. He had destroyed one aircraft and badly damaged the second one—the accident aircraft—in previous encounters with convective weather. Bonanzas are remarkably stout, but nobody builds a match for a severe thunderstorm.

One has to wonder about the psychological background of the pilot, his profession, other hobbies, and his training, although the maintenance shop owner provided a little insight into poor decision making. Most GA accident investigations don’t delve into these factors. Should we invest the considerable additional resources to investigate more deeply? What do we do with that information? The risk tolerance of some pilots is not easily changed, apparently. Are mishaps like this preventable? Share this with any pilot acquaintances who still believe thunderstorms are overrated.