Boeing 727-235 accident at Florida, 8 May 1978

Accident narrative

On May 8, 1978, at about 2120 c.d.t., National Airlines Flight 193, a Boeing 727-235, crashed into Escambia Bay while executing a surveillance radar approach to runway 25 at Pensacola Regional Airport in Florida. The accident occurred during the hours of darkness and in instrument meteorological conditions. The aircraft came to rest in about 12 feet of water approximately 3 nautical miles from the runway. There were 52 passengers and a crew of six on board; three passengers drowned.

**The Flight and Approach Vectors**

Flight 193 was a scheduled passenger flight from Miami to Pensacola, with en route stops that included Mobile, Alabama. The flight departed Mobile at 2102. The captain was flying the aircraft at a cruising altitude of 7,000 feet.

At 2109:20, the flight established communications with the Pensacola radar controller, who advised that they would be vectored for an airport surveillance radar (ASR) approach to runway 25. The controller reported the Pensacola weather as a measured ceiling of 400 feet overcast, with 4 miles visibility in fog and haze. The flightcrew asked if the instrument landing system (ILS) to runway 16 was in use and was told it had been out of service for several months because of construction.

Flight 193 was vectored behind another Boeing 727, Eastern Flight 117. At 2111:14, the controller broadcast to both aircraft that the published minimum descent altitude (MDA) was 480 feet and the missed approach point was the runway threshold. The cockpit voice recorder (CVR) showed that the first officer correctly briefed the captain on the approach minimums and the missed approach procedure.

At 2113:39, the controller cleared Flight 193 to descend to 1,700 feet. The controller then advised that a Twin Beech on an ASR approach had broken out at 450 feet indicated. The first officer noted on the flight deck that 480 feet was the MDA and that 450 feet was "illegal for that runway."

Between 2115:07 and 2118:25, the flight was given a series of vectors, turning to headings of 110 degrees, 160 degrees, and 220 degrees. The descent and in-range checklists were completed, and the crew began the before-landing initial checklist. At 2118:31, the captain called for 15-degree flaps.

At 2119:01, the flight was cleared to descend to 1,500 feet. At 2119:20, the controller advised Flight 193 that it was five and one-half miles from the runway and cleared it to continue to the MDA. At 2119:37, the controller turned the flight to 250 degrees. The flaps were extended to 25 degrees at 2119:49.

**The Final Descent and Impact**

At 2119:54, the controller advised Flight 193 that it was 4 nautical miles from the runway and that Eastern 117 had executed a missed approach. Two seconds later, the landing gear warning horn sounded. At 2120:00, as the aircraft rolled out on the final approach heading, the captain called for the landing gear and the landing final checklist.

At 2120:11, responding to the flight engineer's checklist challenge, the first officer stated the gear was down. This coincided with a transmission from the controller that the flight was on course and 3 1/2 nmi from the runway.

At 2120:15, the ground proximity warning system (GPWS) sounded, broadcasting a "whoop" and a "Pull up, pull up" voice warning. The warning continued for nine seconds. During this period, the CVR recorded the captain asking, "Did you (get) your thing," and the first officer stating, "Descent rate's keeping it up." The flight engineer activated the GPWS inhibit switch, stating later that he did this in response to what he believed was the captain's command to turn the system off.

At 2120:31, the first officer stated they were down to 50 feet. Two seconds later, the aircraft hit the water.

**Evacuation and Survival**

The aircraft struck the bay with its landing gear down and flaps extended to 25 degrees. The impact buckled and crushed the underside of the fuselage, and the underside of the fuselage from fuselage station 950E aft separated from the aircraft. The nose and main landing gears separated during impact. There was no fire.

The aircraft began to fill with water immediately and sank tail-first until the top of the fuselage was awash. The aircraft was not equipped with, nor required to be equipped with, liferafts or approved flotation seat cushions. Many passengers were unaware of the location of the under-seat life vests, and rising water compounded the difficulty of extracting them. Fourteen passengers tried to use seat cushions for flotation, with several reporting that the cushions came apart and were not buoyant.

None of the four door-mounted emergency evacuation slides inflated. Passengers and crew evacuated through overwing exits and doors into the water. The crew and able-bodied passengers assisted others in leaving the aircraft and donning life vests. A tugboat and barge, which had been operating near the extended runway centerline, maneuvered to the aircraft and rescued most of the survivors within 30 minutes.

Post-mortem examinations of the three deceased passengers determined the cause of death in each case was drowning. None had sustained traumatic injuries.

**What the Investigation Found**

**Wreckage and Instruments** Functional testing of the recovered altimeters, radio altimeters, air data computer, and GPWS warning box disclosed no evidence of pre-impact malfunctions. The aircraft's maintenance log contained no outstanding discrepancies, though maintenance alert cards noted that the No. 1 engine was hard to get out of reverse and that all three engines were slow to spool up. The Board noted that since the accident could not be attributed to a failure of any engine to respond to a request for thrust, the reported engine difficulties were not considered contributory.

Documentation of the cockpit revealed the landing gear lever was down and the flap handle was in the 25-degree detent. Both the captain's and first officer's flight directors were in the heading mode. The altitude alerter was set to 2,000 feet. Both barometric altimeters were set to 29.94 inHg with the MDA bugs set at 480 feet. Both radio altimeters were set to the proper MDA.

**Aircraft Performance and Flight Recorders** Flight data recorder analysis showed the descent rate was less than 1,000 feet per minute (fpm) until the aircraft descended through 1,300 feet. The rate then increased to 1,500 fpm, reached 2,000 fpm at 500 feet, and decreased to 1,250 fpm over the last 100 feet. The GPWS activated at about 500 feet, almost coincident with the maximum descent rate.

The performance analysis indicated the final descent from 1,700 feet began with thrust reduced to 25 percent of takeoff rated thrust. Thrust was progressively reduced until it reached flight idle at 940 feet, where it remained for the final 35 seconds of the flight. The pitch attitude decreased from 3 degrees noseup at 1,700 feet to 3 degrees nosedown at 1,250 feet. At 500 feet, the pitch attitude decreased to 4 degrees nosedown until about two seconds before the GPWS warning stopped, at which point the nose was raised, reaching a noseup attitude at impact.

The Board computed that if a go-around had been initiated from the 2,000 fpm descent rate using applied stick forces producing a 1.62 G load factor, level flight would have been attained in 4.2 seconds with an altitude loss of 86 feet.

**Air Traffic Control Procedures** The Board examined the radar controller's adherence to the Air Traffic Control Handbook. The handbook required controllers to vector arriving aircraft to intercept the final approach course at least 2 miles outside the approach gate, which for runway 25 would be 8 miles from the threshold. The controller vectored Flight 193 to intercept about 5 miles from the runway.

The handbook also required the controller to issue advance notice of where the descent would begin. The controller did not provide this notice, testifying that he felt it did not apply because he had already cleared the flight to the MDA before it reached the descent point. The Board concluded that clearing the flight to the MDA half a mile before the descent point did not comply with the intent of the procedure, which is to afford the pilot preparation time to configure the aircraft. The Board found that the controller's nonstandard procedures accelerated the pace of the crew's cockpit activities and made the approach more difficult to accomplish.

**Ground Proximity Warning System** The GPWS on the aircraft featured Mode 1 (excessive descent rate) and Mode 4 (nonlanding configuration below 500 feet). The Board noted that because of the altitude at which the warning began, it was impossible to determine which mode caused the activation, but once below 500 feet, Mode 4 would have sustained the alarm until the flight engineer inhibited the system.

Company procedures stated that if a GPWS warning sounds while maneuvering for an approach at night or in instrument conditions, positive action to alter the flightpath should be initiated immediately if there is any doubt as to the validity of the warning. The captain testified that he believed he was at 1,500 feet when the warning began, so he did not make drastic corrections or add power, but merely eased the yoke back. When the warning ceased—because the engineer inhibited it—the captain erroneously concluded the problem was solved. The Board noted that for 4 to 6 seconds after the warning was silenced, the captain could have arrested the descent and avoided the crash.

**Altimetry and Crew Coordination** The captain testified that he delayed extending the landing gear to avoid placing a simultaneous demand on the hydraulic system while the flaps were in transit. Because of this delay, the landing flaps (30 degrees) were never extended, and the before-landing final checklist was delayed.

The company flight manual required the pilot-not-flying to call out altitudes at 2,000 feet, 200 feet above MDA, 100 feet above MDA, and at MDA, as well as any excessive deviations from the desired sink rate. The first officer made none of these callouts during the final descent. The first officer testified that he was distracted by a red light outside the aircraft and that his "internal time clock" led him to expect they were at 1,000 feet when he looked back at his altimeter. He stated he initially read the altimeter as 1,100 feet because that was what he expected to see.

The captain testified that he misread his altimeter at 500 feet, believing he saw 1,500 feet. He stated he was looking at the hundred-foot pointer instead of the thousand-foot marker. The Board concluded that the captain focused his attention on the vertical speed indicator and either did not look at his altimeter or did not perceive its reading. The Board also noted that the captain continued to use his flight director for heading guidance during the descent, which required him to interpolate the portrayal and likely caused him to devote a higher percentage of his eye scan time to the flight director indicator at the expense of other flight instruments.

Neither pilot recalled observing the MDA warning lights, and neither checked their radio altimeters. The Board believes that the activation of the GPWS directed both pilots' attention to the bright GPWS pullup lights and their vertical speed indicators, which may have prevented them from seeing the MDA lights. The Board stated that an experienced flightcrew should have checked their radio altimeters, which would have provided an immediate readout of absolute altitude.

**Probable Cause**

The National Transportation Safety Board determined that the probable cause of this accident was "the flightcrew's unprofessionally conducted nonprecision instrument approach, in that the captain and the crew failed to monitor the descent rate and altitude, and the first officer failed to provide the captain with required altitude and approach performance callouts. The crew failed to