When early Lear Jet employees get together to reminisce, the conversation invariably gets around to "the accidents." While there were a total of six Lear Jets lost through the end of 1966, the "accidents" refer to three specific incidents where the causes were unknown.
The first occurred 10-21-65. The airplane was owned by Bob Graf of Florida, it was leased back to the company for transportation and demos. The crew dropped a company executive at Detroit and were returning to Wichita when they crashed near Jackson, Michigan. Both were killed.
The second occurred 11-14-65. The airplane was owned by Flying Tiger Airlines. The flight originated at Palm Springs, California with Burbank as the destination. It crashed shortly after takeoff. The crew and six passengers were killed. One of the passengers was the son of Bob Prescott, founder and president of Flying Tigers, also a family friend of Bill Lear.
The third occurred April 23, 1966. The airplane was owned by Rexall Drug. It crashed near Clarendon, Texas. The Rexall pilot was on a check ride with an FAA pilot. Both pilots were killed.
A probable cause for the second accident emerged fairly quickly and it was eventually confirmed by the National Transportation Safety Board. The pilot was 62 year old Paul Kelly, though he only had 125 hours in the Model 23,he had logged over 15,000 hours total time. His co-pilot was a pick up 160 hour private pilot.
The airplane left Palm Springs in marginal weather with the intent of staying VFR while waiting for an IFR clearance to Burbank. It crashed less than 15 miles from the airport. Probable cause, pilot error.
Causes for the other two would never be known for certain. Both airplanes crashed during climb out, both were in rain before climbing into sub-zero conditions at altitudes. The airplanes did not carry any type of flight recorders. There were no clues at the crash site.
While there were some suggestions that the fleet should be grounded until a cause determined, that did not happen. Internally, the company went through a complete detail review of every aspect of the aircraft, a complete "what if?" program. What if this or that happened? A lot of engineering changes were made but no one was certain the problem was fixed.
During this period and unrelated to the investigation, Flight Test was trying to improve longitudinal handling characteristics. Small aluminum strips were attached to the trailing edge of the elevator to try to increase sensitivity.
The airplane was flown by Jim Kirkpatrick. Don Grommesh was in the cabin monitoring an oscillograph checking for damping of the flutter mode. Kirk would take the airplane up to a given speed, trim it out then bump the control wheel with the palm of his hand. Accelerometers on the elevator would send a signal to the cabin to record their position. Grommesh would watch the traces on the oscillograph "up-down-up-down-up-down" making sure the elevator movement was damping (getting smaller) with each cycle.
Neutral damping and the crew would be flirting with disaster. If the elevator excursions go divergent ie. getting bigger with each cycle, it would be classic flutter...the airplane could shake itself apart in a fraction of a second. After each bump of the wheel, Kirk would increase the speed and repeat the test. Damping decreases with increased speed.
Kirk went one bump too many and the airplane did encounter classic flutter. Avionics in the nose shook loose, rivets were sheared, aircraft structure bent. The airplane was still flyable, Kirk landed at Ponca City, Oklahoma. It was the last time the airplane would fly. It is now on display at the Smithsonian in Washington.
An investigation revealed that after the strip was added to the trailing edge, the aircraft was released for flight without re-balancing the elevator. There was too much weight aft of the hinge line. Was this the smoking gun related to the two unexplained accidents?
Could it be that rain may have accumulated in the elevator, then frozen during climb? Would that unbalance the elevator and lead to a flutter condition? No one could say for certain that it was the cause, but it was certainly a plausible theory.
Drain holes were drilled in the trailing edge of the elevators and small scuppers were added to create negative pressure to evacuate any water that accumulated in the elevator.
Did the scuppers eliminate the problem or was it one of the other fixes? No one knows for sure but the unexplained accidents went away. In her autobiography, Moya Lear attributed the accidents to water accumulating in the elevator. One might assume her opinion reflected Bill's.