Convair 240 accident at Havana, Cuba, 9 Dec 1948
On December 9, 1948, a Convair 240 operated by Pan American Airways was involved in an aviation accident near Havana, Cuba. Investigators recorded the probable cause as: "inability to stop the aircraft under marginal conditions of stopping distance because of inadequate braking effectiveness. This summary draws on records from the U.S. Civil Aeronautics Board (CAB) accident report collection at the National Transportation Library; 8 related events involving the same aircraft type or operator are linked below.
Probable cause
"inability to stop the aircraft under marginal conditions of stopping distance because of inadequate braking effectiveness.
— NTSB Determination
Accident narrative
On December 9, 1948, at approximately 1726, a Pan American Airways Convair 240 crashed at Rancho Boyeros Airport in Havana, Cuba, during an attempted takeoff. The aircraft rolled off the end of the runway and struck a ditch. The stewardess was slightly injured; all of the other occupants were unhurt.
**The flight**
Flight 428 was the return portion of a scheduled trip from Miami, Florida. The crew consisted of Captain Thuel V. Schuhart, First Officer Henry W. Brotherton, Purser Richard Abbott, and Stewardess Betty Jean Poe. Captain Schuhart had logged 4,210 flying hours, including 387 in the Convair 240. First Officer Brotherton had 2,616 hours, with 6 hours in the Convair 240. The aircraft's gross weight was 38,921 pounds, which was within allowable limits.
**The takeoff**
The flight was cleared to taxi to Runway 5. During the pre-flight check, the right engine fluctuated and backfired several times when operated on the right magneto. The crew operated the engine at 30 inches of manifold pressure until the cylinder head temperature increased to 200 degrees Centigrade. Upon retesting, the magnetos and engines operated within normal limits.
The first officer, seated on the right, began the takeoff run. At a speed of approximately 95 knots, back pressure was applied to the controls to lift off. At this time, the captain sensed an unusual vibration. He took over control, closed the throttles, and applied the brakes.
The aircraft had traveled about 2,600 feet down the 4,500-foot runway when the brakes were applied. Within a short distance, the left outboard and right inboard tires blew out. With the aircraft's speed still fairly high, the captain applied the emergency air brakes. The aircraft failed to stop, rolling off the paved runway and continuing 300 feet to the airport boundary, where it struck a drainage ditch and skidded to a halt 315 feet beyond the boundary.
The weather was a high overcast with unlimited visibility and a 6-mile-per-hour wind.
**What the investigation found**
The aircraft was extensively damaged, and fire had substantially destroyed the right engine nacelle and a large portion of the right wing. The nose and left main landing gears had failed and folded rearward, while the right gear remained extended and locked.
Investigators examined the runway and found heavy marks from the left outboard wheel beginning 2,600 feet from the start of the runway, with marks from the other tires indicating skidding action. The left inboard and right outboard brake linings were badly worn and pitted, indicating they had been subjected to intense frictional heat. The left inboard tire showed little wear and moderate braking action throughout the run.
The Board noted that at 95 knots, the aircraft was nearly airborne, making it easily possible to lock the wheels and cause the tires to skid and blow out. The Board believed that completing the run with only two wheels capable of normal braking may have contributed to the failure to stop, and that heavy brake application could have caused them to overheat and become less effective. Civil Aeronautics Administration tests indicated that at the aircraft's weight and speed, it could have been stopped in 1,552 feet using brakes alone, though the Board concluded blown tires would increase this distance.
The captain had applied the emergency air brakes during the rollout; the investigation noted that while these were standard equipment, the pilots had received no training in their use other than written instructions.
The cause of the unusual vibration was not determined. A nosewheel shimmy or unbalanced tire were considered possible causes, but a test flight of another Convair using the damaged aircraft's nosewheel assembly and similarly worn tires produced no vibration. The right engine's backfiring was determined to be caused by low cylinder head temperatures before the run-up.
The aircraft's flaps were found fully retracted. The crew stated they had lowered the flaps prior to takeoff and did not remember raising them. The Board noted they may have been raised unconsciously, as the company's training procedure for aborted takeoffs included flap retraction.
The aircraft was equipped with reversible propellers, but the carrier had made this feature inoperative. The Civil Aeronautics Administration had certificated the aircraft for this route without the use of reversible propellers. However, following the accident, Pan American Airways concluded the braking system was critical under certain conditions and initiated modifications, including reinstating propeller reversing, installing high-capacity brakes, and checking pilots in the actual use of air brakes.
**Probable cause**
The Board determined that the probable cause of this accident was "inability to stop the aircraft under marginal conditions of stopping distance because of inadequate braking effectiveness."