McDonnell Douglas DC-10-10 accident at Florida, 8 Jul 1974

Accident narrative

On July 8, 1974, at about 0940 e.d.t., National Airlines Flight 41 experienced an explosion and severe vibrations during climbout from Miami International Airport in Florida. Cowling from the No. 1 engine separated, damaged the left wing, and was ingested into the No. 2 engine. The flightcrew made an immediate emergency landing at Tampa International Airport. None of the 172 people on board were injured.

### The flight

Flight 41 was a scheduled nonstop trip from Miami to Los Angeles International Airport, carrying 160 passengers and 12 crewmembers. The McDonnell Douglas DC-10-10 departed Miami at 0914.

As the aircraft climbed through 25,000 feet, an explosion and severe vibrations shook the airplane. The vibrations were so severe that the flightcrew had difficulty interpreting their instruments. The captain determined there was a problem with the No. 2 engine and retarded its throttle toward the idle position. Simultaneously, the flight engineer noticed a complete loss of No. 2 hydraulic and oil systems pressure, as well as the loss of the No. 2 electrical bus.

The captain immediately initiated an emergency descent. The first officer contacted the Miami Center, advised them of the problem, and stated their decision to land as soon as possible at Tampa. Shortly after the descent was initiated, the flight engineer observed three separate No. 2 engine fire warning indications. He advised the captain and discharged one No. 2 engine fire bottle, followed by the second bottle 30 seconds later. The fire warning lights went out.

The crew executed a visual descent and approach to the ILS final approach course for runway 36 at Tampa. A visual landing was made at 0951 with no further difficulty. All occupants departed the aircraft through normal exits at the passenger terminal.

### What the investigation found

Inspection of the aircraft revealed that the No. 1 engine core cowl was missing. The separated cowling had torn a 9-by-9-inch hole in the left wing leading edge outboard of the No. 1 engine, and a 6-by-6-inch hole in the upper wing surface. The No. 2 engine sustained extensive internal and external damage, a section of its cowl was missing, and the vertical stabilizer was dented.

The Safety Board investigation found that the aircraft had been routed to maintenance two days earlier, on July 6, because of a pilot complaint that the No. 1 reverser lock light remained on after landing. Line maintenance personnel removed the No. 1 engine core cowl to replace the fan reverser.

After the reverser was replaced, mechanics set the inboard section of the core cowl in place with only the center mounting bracket bolt inserted, and no nut was placed on this bolt. The off-going mechanics verbally notified the oncoming shift of the incomplete work before leaving.

Personnel on the next maintenance shift did not go immediately to the aircraft, as two other DC-10s required maintenance to meet flight schedules. When they returned, despite the verbal turnover, they assumed all three inboard core cowl retaining bolts had been properly installed and secured, and proceeded to close and latch the assembly. Investigators found no entry in any maintenance forms indicating the removal of the core cowl or fan reverser, which violated company manuals requiring removed panels to be logged on a standard Maintenance Supplement.

The repair was supervised by line maintenance personnel for about five work shifts. The discrepancy was not corrected because the aircraft was needed for passenger service, and it was dispatched on July 8 with the original complaint listed as an open item.

Because there was only minor damage to the inboard core cowl mounting brackets, the Board determined that the inboard half of the core cowl separated first, and that the resulting air loads tore the outboard panel from its mounting brackets. The Board concluded that the cowl separated in flight because it was not attached properly after the maintenance work.

### Probable cause

The National Transportation Safety Board determined that the probable cause of the accident was "the failure of company maintenance personnel to complete the installation of mounting bolts on the inboard panel of the No. 1 engine core cowl. This failure resulted from noncompliance with established company maintenance procedures."