Cessna 402C, Vieques, Puerto Rico, July 8, 2000–“One main landing gear tire, wheel and brake assembly, the left wing lower skin from the area above the wing flap, the left wing baggage compartment door, the right nose baggage compartment door, the cabin floor cover and some items from the U.S. mail cargo airplane were recovered floating in the ocean…The remainder of the airplane was not located [or] recovered.” The NTSB’s final report concludes the Cessna twin’s final flight was caused by “the airplane’s entry into an uncontrolled descent for undetermined reasons from which it crashed into the ocean.”

On a Part 135 non-scheduled domestic mail contract mission, the flight departed San Juan, Puerto Rico, heading for St. Croix, U.S. Virgin Islands. San Juan Approach Control (operated by the FAA) identified N405MN on radar shortly after 0430 and issued a climb to 7,000 ft. Both the FAA’s San Juan Approach Control and the U.S. Air Force radar data show the 402 leveled at 7,000 ft around 0444. About a minute later, the controller cleared N405MN direct to St. Croix. The pilot requested radar vectors to St. Croix and he received a heading of 140 deg.

At 0453:26 the pilot requested a lower altitude and was cleared to 2,000 ft. He acknowledged the descent clearance but ATC received no further transmissions.
The radar data showed the initial descent began at 0454. Within 30 sec the aircraft was through 6,500 ft. At 0454:41 radar data showed 5,600 ft and eight seconds later through 4,000 ft. The last radar return was four seconds later and the aircraft’s transponder showed 1,100 ft. “No other aircraft or radar returns were observed near the flight as it began its descent,” the NTSB determined.

Some five miles north of the 402’s last radar position, about 11 hr later, the U.S. Coast Guard found debris and mail. They estimated the sea depth around the accident to be 6,000 ft. Although they recovered components on the aircraft, neither the main airplane wreckage nor the pilot was found. The NTSB found no evidence of fire, heat or soot damage on the pieces recovered. According to investigators, they recovered and identified a mail pouch weighing 75 lb as cargo placed on the accident aircraft.

Weather did not seem to be a factor in the accident, although both the sun and the moon were below the horizon. St. Croix reported clear skies and 10 mi visibility. Roosevelt Roads NAS reported visibility greater than six miles, few clouds at 2,500 ft and ceilings of 11,000 ft broken and 25,000 ft broken. Pilots flying around the time and place of the accident reported scattered showers and clouds.

N405MN was a 1980 Cessna 402C, owned and operated by M&N Aviation and flown by a commercial pilot rated for single and multi-engine land airplanes and for instrument flight. According to the operator, the pilot had 2,400 hr TT and 1,980 hr multi-engine. He had 235 hr in type.

The aircraft had 13,702 hr total flight time and passed a 100-hr inspection 10 days before the accident. It was within the 24-calendar-month period for IFR checks. Twelve flight hours and five days before, the mechanics changed the left propeller. After an incident at Vieques in April last year, pilots ferried the aircraft for skin repairs to the right leading edge, aileron and tip. The 402 flew 86 hr afterward without incident. Investigators estimated the aircraft’s weight and balance was within limits.