In less than a minute, the aircraft ballooned 500 feet above assigned altitude, then plunged 3,500 feet below it. Power was idle to avoid redlining the airspeed, but VNE was exceeded anyway. The rain noise was so loud that the two pilots could barely hear each other, but more alarming was the turbulence, icing, and uncontrolled rolling of the aircraft beyond 70 degrees of bank.
Forget about notifying air traffic control. Just maintaining wings-level flight took the physical efforts of both pilots. Anyway, the only sound issuing from the radios was static.
Then the windshield froze over. “I tunneled out for maybe five seconds while I was trying to wrap my head around what was going on,” one of the pilots recalled.
The aircraft was in the heart of an embedded mature thunderstorm.
If thunderstorms are the menace that every pilot, IFR or VFR, learns to respect at the greatest possible distance, embedded thunderstorms represent the trickiest for an instrument pilot to avoid penetrating.
This ride was experienced by an air carrier flight that had taken routine measures to avoid such an encounter, climbing quickly to altitude, where the flight “was just about to top the weather.” A recent pilot report indicated that the ride through the area was smooth.
Avoidance is king, but “flying in areas where thunderstorms are embedded in large cloud masses may make thunderstorm avoidance difficult, even when the aircraft is equipped with thunderstorm detection equipment. Pilots must be prepared to deal with inadvertent thunderstorm penetration,” says Appendix A, “Emergency Procedures,” of the Instrument Procedures Handbook.
Reviewing that section reminds pilots that “as with any emergency, the first order of business is to fly the aircraft. The pilot workload is high; therefore, increased concentration is necessary to maintain an instrument scan.”
Once a thunderstorm is penetrated, standard advice is to maintain a course straight through. Why?
The quickest exit may be the most direct passage through the cell. Also, “turning maneuvers only increase structural stress on the aircraft.”
Fly at the aircraft’s recommended turbulence-penetration airspeed, minimizing power changes.
Icing is always possible in thunderstorms, so activate anti-icing or deicing equipment (including pitot heat).
The outcome of the Aviation Safety Reporting System narrative recounted here? Happily, the crew, struggling against severe turbulence, icing, and loss of altitude and bank control, prevailed.
“A little after that we saw blue sky and headed for it,” the report said.