Douglas DC-9-32 accident at Atlanta, Georgia, 7 Jan 1996

Accident narrative

On January 7, 1996, at about 1620 central standard time, ValuJet Airlines flight 558, a Douglas DC-9-32, touched down hard in the approach light area short of runway 2R at Nashville International Airport in Tennessee. The flight was a scheduled domestic passenger trip from Atlanta, Georgia. Of the five crewmembers and 88 passengers on board, one flight attendant and four passengers reported minor injuries. The airplane sustained substantial damage to its tail section, nosegear, aft fuselage, flaps, slats, and both engines.

### The flight

The flightcrew consisted of a captain and a first officer. The captain had 4,381 total flight hours, including 1,061 hours in the DC-9, with 26 hours as a DC-9 captain. The first officer had about 7,707 total flight hours, with 205 hours in the DC-9. The first officer performed pilot flying duties for the trip. Visual meteorological conditions prevailed for the instrument flight rules flight plan.

### Departure and in-flight anomaly

The flight departed Atlanta at 1525, delayed in part by auxiliary power unit maintenance and deicing operations. The captain stated that during his exterior preflight inspection, the nosegear strut inflation appeared normal. The pilots reported that the engine start and taxi were normal, though they encountered ice and snow and were concerned about surface contamination.

After takeoff, the first officer requested the landing gear up, but the captain found the lever would not move beyond the uplock check position. Following the company's quick reference handbook (QRH), the captain attempted to turn the nosewheel steering wheel. It did not turn, indicating a malfunction of the landing gear anti-retraction mechanism. The pilots pushed the landing gear handle release button and raised the lever, and the gear retracted.

As the airplane climbed through 4,000 feet, the takeoff warning horn sounded and the first officer noted the cabin was not pressurizing. The flightcrew consulted the QRH again and determined the ground shift mechanism must have malfunctioned. The ground shift mechanism, actuated by nosegear shock strut extension, controls whether certain aircraft systems operate in the ground or flight mode. The QRH stated that pulling the ground control relay circuit breakers (H20 and J20) would place the electrical circuits in the flight mode. The pilots stated that when the first officer pulled the breakers, the horn silenced and the cabin began to pressurize.

The ValuJet company operating manual (COM) stated that pilots shall report all incidents or irregularities to company system operations or dispatch at the earliest opportunity. The pilots indicated they did not contact dispatch about the anomaly, believing ice and snow had contaminated the mechanism and that they had resolved the problem. They planned to have contract maintenance personnel examine the airplane in Nashville.

### Approach and hard landing

During the en route descent, the flightcrew consulted the QRH for approach and landing procedures. The pilots decided to depressurize the cabin during the descent and, to preclude a loss of cabin pressurization after touchdown, to reset the ground control relay circuit breakers just before touchdown.

The first officer flew the instrument landing system approach to runway 2R. The flightcrew stated the landing gear extended normally and flaps were fully extended. The first officer told investigators that at about 100 feet above ground level, the captain reset the ground control relay circuit breakers. The first officer reported hearing the sound of the ground spoilers deploying as the airplane began to descend at an excessive rate. He shouted "ground spoilers!" and attempted to arrest the sink rate with back pressure and full power.

At about 1620, the DC-9 struck the runway approach light area tail first, followed by the main landing gear and nosegear. The nosewheel tires and rims separated, and the airplane became airborne again. The captain assumed control and established a climb. The flightcrew left the landing gear extended and raised the flaps to 15 degrees.

### Return and second landing

During the go-around, the pilots noticed that the No. 1 communication radio and the No. 2 communication and navigation radios were unusable. Unable to communicate with air traffic control, the first officer tuned the transponder to 7700 and 7600, indicating a distress situation and lost communications. The pilots agreed to remain in visual conditions and return to land on runway 31.

The pilots stated they did not arm the spoilers for the second landing, planning to deploy them manually. At about 1628, the airplane touched down on runway 31. Both pilots stated they heard a loud grinding noise when the nosegear touched down, and the airplane drifted left. The captain corrected with brakes, stopping the airplane about 5,800 feet from the approach end. The passengers deplaned via the left front airstair onto buses.

### What the investigation found

The Board concluded that the nosegear shock strut extension during the initial climbout was insufficient to actuate the ground shift mechanism, release the gear lever anti-retraction mechanism, and shift the airplane systems to the flight mode. Douglas representatives indicated this is a commonly reported occurrence during cold weather operations when the strut is underserviced or underinflated. The Board found that ValuJet's maintenance manual did not contain nosegear shock strut servicing procedures that reflected the guidance provided by Douglas for cold weather operations. The Board also concluded that preflight visual inspections by flightcrews cannot be relied upon to detect underserviced DC-9 nosegear struts.

The investigation reviewed ValuJet's manuals and training. The Board noted that the QRH instructed pilots to reset the ground control relay circuit breakers under the "Approach and landing" heading, but did not specify when. The more detailed aircraft operating manual (AOM) specified resetting them "during taxi". The pilots reported using only the QRH, stating they were encouraged during simulator training to use it as their primary source for abnormal procedures.

The Board concluded the flightcrew's decisions and actions demonstrated insufficient concern for adherence to company guidance. The Board noted that the captain allowed the first officer to fly despite a COM limitation requiring the captain to have 100 hours in type to do so, and that the crew failed to contact dispatch about the in-flight irregularity. Had they contacted dispatch, the Board concluded they probably would have received sufficient guidance to land uneventfully.

Postaccident examination revealed the radio failures during the go-around were the result of the initial ground impact. The No. 1 radio switch was in an unpowered position, likely bumped during the impact or go-around, and the right DC bus reverse current relay in the nose wheel well had opened.

The Board also noted that the cockpit voice recorder (CVR) was a 30-minute closed loop tape. Because electrical power remained on for about 36 minutes after the hard landing, the recording of the initial approach, the hard landing, and the go-around was overwritten. The Board concluded this 30-minute duration was inadequate and hindered the investigation.

The Board concluded that the Federal Aviation Administration's oversight of ValuJet was inadequate, noting that the principal operations inspector and principal maintenance inspector approved the winter operations portions of the manuals even though they lacked cold weather servicing procedures for the nosegear shock strut.

### Probable cause

The National Transportation Safety Board determined that the probable cause of this accident was "the flightcrew’s improper procedures and actions (failing to contact system operations/dispatch, failing to use all available aircraft and company manuals, and prematurely resetting the ground control relay circuit breakers) in response to an in-flight abnormality, which resulted in the inadvertent in-flight activation of the ground spoilers during the final approach to landing and the airplane’s subsequent increased descent rate and excessively hard ground impact in the runway approach light area."

Contributing factors were "ValuJet’s failure to incorporate cold weather nosegear servicing procedures in its operations and maintenance manuals, the incomplete procedural guidance contained in the ValuJet quick reference handbook, and the flightcrew’s inadequate knowledge and understanding of the aircraft systems."