Tuesday, October 5, 2010
Hazards Of Extreme Flying
You have to know when you’re too close to crossing the line
The pilot had telephoned flight service to be briefed for an IFR flight to Mobile, Ala. The briefer warned of a line of embedded thunderstorms along the route from Atlanta to Mobile including SIGMETs and advised that tops were forecast to be at 41,000 to 50,000 feet. The specialist suggested that the pilot might land at an intermediate stop ahead of the weather, possibly in Pensacola, Fla., or farther north in Crestview, Fla., wait for the storms to pass and then continue the flight to Mobile. The pilot filed an IFR flight plan from Cornelia, Ga., to Pensacola at 16,000 feet. The pilot then called back to obtain his clearance. The flight service specialist put the pilot on hold while he worked out a void time with ATC. When the specialist picked up again, the pilot was no longer on the line.
The pilot departed Cornelia without an IFR clearance and contacted Atlanta ARTCC. The controller advised the pilot that he wasn’t on his assigned heading, altitude or correct transponder code, and subsequently handed the pilot off to another controller. The flight was subsequently cleared direct to Panama City, Fla., and the pilot was instructed to climb to 16,000 feet. The pilot then radioed that “...we’re going to make a reverse.” The controller responded, “Roger,” and there were no further communications.
Radar data showed that the airplane was level at 16,000 feet heading southwest, and then began a continuous left turn northwest-bound and descended to 15,700 feet, then 15,600 feet, then dropped off radar.
Atlanta ARTCC had broadcast weather alerts for the route the accident airplane was following over the radio frequency the pilot was on. There was a line of thunderstorms 40 nm wide, and moving from 280 degrees at 35 knots. The tops of the thunderstorms were at 44,000 feet, with two-inch hail and possible wind gusts up to 60 knots.
A weather study conducted by the NTSB revealed the pilot penetrated an intense to extreme VIP level-5 to level-6 weather radar echo. The thunderstorm contained strong horizontal and vertical winds, heavy rain, turbulence, icing and instrument flight conditions. The cloud tops of the cell the Aerostar penetrated were near 38,000 feet and the freezing level was near 14,000 feet.
The NTSB found that the controllers failed to comply with FAA directives regarding the issuance of severe weather information by not advising the pilot of the weather displayed on the radar controller’s scope. According to the recorded display system information, the controllers should have been able to see that there was moderate to extreme weather depicted along the airplane’s flight track.
The airplane’s Pilot’s Operating Handbook says that, in turbulent air, the pilot should reduce airspeed to 166 knots indicated or less and fly attitude (autopilot altitude hold off) and avoid abrupt maneuvers. It continues, “In conditions of extreme turbulence, reduce airspeed to maneuvering speed or slightly less. Maneuvering speed decreases with the weight of the airplane—e.g., 166 KIAS at 6,000 pounds and 152 KIAS at 5,000 pounds. A reduction in airspeed will lower the stress to which the airplane is subjected by turbulence. Fly attitude and avoid abrupt maneuvers. Fasten seat belts and shoulder harness securely as a precaution against buffeting and lurching. When flying in extreme turbulence or strong vertical currents and using an autopilot, the altitude-hold mode should not be used.”
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