Douglas DC-6B accident at Laguardia Airport, New York, 5 Jun 1964

Accident narrative

On June 5, 1964, Northeast Airlines Flight 715, a Douglas DC-6B, struck a water retaining dike during a visual landing approach to runway 31 at LaGuardia Airport in New York. The aircraft's two main landing gears separated upon impact, but the airplane remained upright and slid to a stop on the runway. There was no fire, and the 39 passengers and four crew members evacuated without injury. The Civil Aeronautics Board determined the probable cause was the captain's failure to properly plan and execute the final approach.

### The flight

Flight 715 was a regularly scheduled passenger service from Lebanon, New Hampshire, to New York City, with a stop in Boston, Massachusetts. A scheduled crew change took place in Boston. Captain Karl F. Ritz had 13,661 total flying hours, including 3,390 in the DC-6B. First Officer Gaetano M. Zompetti had 6,617 total hours, with 3,390 in the DC-6B, and Flight Engineer John R. Riffle had 4,013 hours, including 2,768 in the DC-6B.

The flight departed Boston at 1133 on an Instrument Flight Rules (IFR) clearance. Approaching the New York area in visual flight conditions, the crew canceled their IFR flight plan. LaGuardia approach control informed the flight that runway 31 was in use and provided a current Notice to Airmen (NOTAM) stating the landing length was restricted to 5,813 feet due to men, heavy equipment, and cranes at the departure end.

### The approach and accident

Over New Rochelle, the flight contacted the LaGuardia Tower and was instructed to report over the field. The captain stated that flaps were extended to 20 degrees at an altitude of approximately 4,000 feet. The aircraft was turned onto the downwind leg about 1.5 miles west of the airport at 3,500 feet. The tower cleared the flight to land, noting that the aircraft appeared to be "high" in the traffic pattern.

The crew lowered the flaps to 25 degrees on the downwind leg, turned onto the base leg at approximately 2,000 feet, extended the landing gear, and lowered the flaps to 30 degrees. Turning onto the final approach, the propellers were advanced to 2300 rpm, and flaps were lowered to 40 degrees at approximately 1,000 feet.

Runway 31 was equipped with a Visual Approach Slope Indicator (VASI), which uses arrays of red and white lights to provide visual glidepath guidance. The captain stated that at 1,000 feet, both sets of VASI light bars indicated white, meaning the aircraft was above the glidepath. At an estimated 1.5 miles from the runway and 600 feet in altitude, the captain observed the upwind lights change from pink to red while the downwind lights remained white, indicating the aircraft was on the proper glidepath. He stated he then decided to utilize the VASI lights to establish the final approach flightpath, adjusting his rate of descent to remain on the VASI at an airspeed of about 120 knots.

Approaching the runway threshold, the captain called for 50 degrees of flaps. The first officer placed the selector lever in the 50-degree detent, which the flight engineer verified. The captain fully retarded engine power and raised the nose to reduce airspeed from 115 knots to 100 knots. He stated his visual observations of the VASI lights were then limited to the downwind units, which remained steady white.

As the aircraft passed over the water retaining dike—located about 250 feet ahead of the runway threshold and standing approximately six feet above the runway surface—the crew heard and felt a "thump." The captain stated he thought the landing gear was still with them, while the first officer remarked they might have blown a tire.

Both main landing gear wheels had struck the dike about one foot below its top. The entire right main landing gear assembly, along with the wheel axle and lower strut components of the left main gear, separated from the aircraft. The airplane touched down on its left main shock strut 1,164 feet from the threshold, and the aft fuselage contacted the runway at 1,800 feet. The aircraft slid down the runway, coming to rest just off the right edge 3,400 feet from the threshold. The passengers evacuated via the main cabin door within an estimated two minutes.

### What the investigation found

Investigators found the nose landing gear intact and locked down. The wing flaps were found in the 20-degree extended position, and the cockpit flap selector lever was in the full up position. However, tire marks matching the main landing gear wheels were found on both flaps, and the left inboard flap actuator rod had a bend.

The Board noted this damage occurred when the aircraft contacted the runway, exerting an upward force on the flaps. The bend in the rod indicated the flaps were necessarily extended more than 20 degrees when the damage occurred. The Board believed the flaps were in the full down or near full down position at impact, and that the 20-degree position found at the wreckage was attained subsequently, likely due to inadvertent placement of the selector lever during the crew's hurried egress or an interruption of hydraulic pressure. The Board believed there was no change in flap position prior to impact that would have caused an unexpected loss of altitude.

The VASI system was ground checked and flight checked by the Federal Aviation Agency following the accident. All elements were found to be operating satisfactorily with a computed glide slope angle of 2.90 degrees. The Board noted that the on-glidepath wedge is 42 feet thick directly above the dike, and the bottom of this wedge is 38 feet above the top of the dike. The distance from the DC-6B pilot's eye level to the bottom of the main landing gear wheels is approximately 13 feet 4 inches.

The Board analyzed that if the aircraft had been flown even at the lowest limits of the proper VASI glidepath, there would still have been approximately 24 feet of clearance between the top of the dike and the bottom of the main landing gear. Because the VASI was operating properly, the Board could not reconcile the captain's testimony of receiving on-glidepath color indications with the aircraft striking the dike. The Board believed the captain did not properly utilize the VASI system during the final phase of the approach, concluding that the aircraft was flown at too low an altitude to allow reasonable clearance of the dike.

### Probable cause

The Board determines that the probable cause of this accident was "the failure of the captain properly to plan and execute the final approach."