Tuesday, March 9, 2010
Safety’s Ideal World
Unfortunately, we don’t always learn from example
The 44-year-old pilot held a private pilot certificate with airplane single-engine land and instrument ratings. He had taken flight training for the PA46-500TP along with a flight review and instrument refresher from a commercial provider. At the time of training, the pilot reported 1,000 hours of total flight time, 300 hours of instrument flight time and 50 hours of turbine flight time.
The POH listed 127 KIAS as the airplane’s maximum operating maneuvering speed (Vo). The limitation associated with Vo stated, “Do not make full or abrupt control movements above this speed.” The POH listed 188 KIAS as the airplane’s maximum operating speed (Vmo). The limitation associated with Vmo stated, “Do not exceed this speed in any operation.”
The switch to turn on pitot heat is located on the right overhead switch panel. The static source ports aren’t heated; if they ice over, selecting the alternate static source is supposed to alleviate the problem. According to the POH, the airplane’s annunciator panel was equipped with an amber caution light that displayed “pitot heat off,” which “indicates the pitot heat has not been selected on.” There also were two red warning lights, one for each of the left and right pitot heads. The red lights come on in the event of a pitot heat failure, such as a burned-out heating element. The POH’s “before takeoff” checklist calls for “pitot heat on.”
According to a Piper representative, the data for similarly equipped Meridians showed an increase in the electrical load of approximately 13 amperes when the pitot heat is turned on. The pitot heat system is designed to cycle itself on and off at a 30-second rate to prevent overheating while the airplane is on the ground with the pitot heat switch selected on. While in flight, the pitot heat operates continually when turned on.
Investigators removed chips from the airplane’s glass-panel avionics, which record data used to generate panel displays. The data revealed that the outside air temperature dropped from 24 degrees C at the surface to zero degrees C at 8:09:41 and 15,900 feet MSL. The pilot’s airspeed data dropped from 142 KIAS to zero at 8:10:45, and the copilot’s airspeed dropped from 140 KIAS to zero at 8:10:51.
The airplane’s climb rate decreased as the airspeed data dropped to zero, and at 8:11, the airplane started a left turn. Airspeed, vertical speed and altimeter data validity bits switched to a fail state. A red “X” is flagged over displayed parameters that have failed validity bits. The pilot’s PFD data was in the flagged fail state between 8:12:13 and 8:12:42. The copilot’s PFD data was in the flagged fail state between 8:10:55 and 08:11:03 and again between 8:11:25 and 8:11:43. The data showed that the airplane’s engine was operational and that there was no reduction in power as the aircraft started the left turn. At 8:12, the data showed that the airplane had achieved a 250-knot groundspeed and then sustained two vertical accelerations of about 5 G’s. The airplane subsequently descended and rolled during its descent. Review of MFD data didn’t reveal any evidence of changes in the plane’s electrical load, which would have been expected if the pitot heat was operating.
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