Grumman G-21A accident at Kodiak Island, Alaska, 24 Dec 1961

Accident narrative

On December 24, 1961, a Kodiak Airways Grumman G-21A amphibian crashed shortly after lift-off during a water takeoff from Old Harbor, Kodiak Island, Alaska. The twin-engine aircraft struck the water, pitched up steeply, and dove back into the bay, breaking apart and sinking. One passenger was thrown from the aircraft and drowned. The pilot and three other passengers were rescued. The Civil Aeronautics Board investigated and determined the crash resulted from an improperly executed takeoff that caused a high-speed porpoise maneuver.

### The flight

The Grumman G-21A, registered N 1503V, was operating a scheduled passenger, mail, and cargo flight. It departed Kodiak at approximately 1000 Alaska Standard Time, with planned en route stops including Old Harbor. The pilot, Gene Ralph Kingston, had accumulated approximately 6,809 flying hours, with about 1,160 in amphibious aircraft. He flew the first leg without passengers.

After a normal water landing at Old Harbor at about 1040, the aircraft was beached and 33 pounds of mail were off-loaded. Four passengers and about 40 pounds of cargo were loaded aboard. Shortly after, the parking brake slipped, causing the aircraft to pivot and entangle its tailwheel in a tubular steel passenger loading ladder. The pilot and bystanders removed the 6-1/2-pound ladder. Because a previous incident had punctured the hull, the pilot crawled underneath to inspect it. Finding no scratches or external structural damage, he completed a routine walkaround inspection, noting the hull drain plugs were secure.

The passengers boarded the aircraft: a boy and two women occupied the cabin, and another boy was seated in the cockpit to the right of the pilot.

### The accident

Weather conditions were unrestricted, with clear skies and calm water. At approximately 1048, the aircraft taxied into the bay. The pilot stated he completed his pre-takeoff checklist and began the takeoff run to the southwest at 1050.

Three ground witnesses observed the takeoff. They described the initial part as normal, but after the airplane gained an altitude of 50 to 150 feet, it descended and struck the water. It immediately rose in a 45-degree climbing attitude to 300 or 400 feet, then nosed over abruptly and dove into the water. Witnesses noted the engines sounded normal and no parts fell from the aircraft. The distance from the start of the takeoff run to the crash site was approximately one mile.

The pilot's account differed regarding the altitude and water contact. He stated he kept the airplane low after takeoff to gain airspeed, a practice used in Alaska to avoid possible turbulence. He recalled the bow starting to rise, prompting him to push the control wheel forward to maintain level flight. He stated the wheel hit the instrument panel with no resistance. As the climb steepened and the bow then began to drop, he pulled back, again feeling no resistance as the wheel hit the backstops. Believing he had suffered a control failure, the pilot reduced power to stop the climb and maintained a gradual nose-low descent, hoping to apply full 60-degree flaps and hit the throttles just before impact. He stated he did not believe the aircraft reached higher than 50 feet or contacted the water before the final crash.

Upon final impact, the seats of the three cabin passengers broke loose. The pilot recalled a downward impact, sinking underwater in his seat, and swimming to the surface. He and the three cabin passengers clung to the floating tailwheel and a life preserver until a boat rescued them. The boy seated in the cockpit was thrown from the aircraft and drowned; his body was recovered approximately 15 feet from the point of impact. The aircraft sank in 75 feet of water.

### What the investigation found

The wreckage was recovered over the following month. The nose section had completely separated at impact at station No. 11. The tail section broke off at station No. 31 but remained attached to the fuselage by several control cables.

Examination of the engines and propellers showed they were capable of normal operation, with throttles and pitch controls found in full power positions. The wing flap selector valve was in the flaps-full-down position. The main fuel selector valve was found in the "off" position, but the Board believed it was moved during salvage operations.

Investigators closely examined the flight controls to address the pilot's belief that the elevator system had failed. Several fractures were found in the aileron, elevator, and rudder systems. At station No. 11, the elevator bellcrank was broken. At station No. 29, a cluster of six pulleys and two axis bolts serving the elevator, rudder, and tailwheel retraction cables had been torn from their brackets in a forward and upward direction.

The Board's detailed analysis determined that the bellcrank and pulley cluster failed from instantaneous overloads. No metal fatigue was found. The Board believed this failure was due to impact forces when the tail section broke off, and that the airplane was mechanically capable of normal operation prior to impact.

The Board also ruled out other factors. Weight and balance were within limits. While temperatures were conducive to spray icing, the Board noted a normal lift-off occurred, making icing an unlikely factor. The possibility of an excessive aft center-of-gravity shift caused by water in the hull was also dismissed, as the hull had been drained, inspected, and verified watertight before impact.

The most probable explanation is that the pilot, intending to level off at a low altitude to gain airspeed, failed to recognize a gradual loss of altitude. This resulted in the aircraft striking the water in a slightly nose-low attitude at high speed, producing a phenomenon known as high-speed low-angle porpoising.

According to Navy hydrodynamic studies cited by the Board, when a flying boat contacts the water at a shallow angle and high speed, the nose is initially sucked deeper into the water. Hydrodynamic forces then reverse and repel the aircraft with a violent thrust upward. This increases the angle of attack and lift, occurring regardless of pilot action. Proper recovery requires maintaining full power and flying the aircraft out of the ascent phase.

Because the pilot did not realize the aircraft had struck the water and entered a porpoise, he erroneously assessed the violent movements as an elevator control failure. The Board noted that his corrective actions—reducing power and using full flaps—were completely incompatible with recovering from a porpoise, eliminating his opportunity to effect a safe recovery before the aircraft stalled and dove.

### Probable cause

The Board determined that the probable cause of this accident was "an improperly executed takeoff which resulted in an inadvertent descent into the water. This produced a high-speed low-angle porpoise from which the pilot was unable to recover."