1973 — July 23, Ozark Air 809 ILS approach into downdraft; crash, St. Louis, MO — 38

–38 Kimura. World Commercial Aircraft Accidents 3rd Ed., 1946-1993, V.1. 4-11-1994, p. 3-19.
–38 NTSB AAR. Ozark Air…Near…Lambert-St. Louis Int. AP…MO, July 23, 1973. 1974.
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Narrative Information

NTSB: “Synopsis

“About 1743 c.d.t. on July 23, 1973, Ozark Air Lines Flight 809, a FH-227B (N4215). crashed 2.3 miles southeast of the Lambert-St. Louis International Airport, i n St. Louis, Missouri. Forty-one passengers and three crewmembers were aboard the aircraft. Thirty-seven passengers and one crewmember received fatal injuries. The aircraft was destroyed by impact and fire.

“While Flight 809 was making an instrument landing system (ILS) approach to runway 30L on Lambert-St. Louis, a severe thunderstorm with heavy rain, strong winds, and roll clouds moved across the approach end of the runway and localizer course from the southwest. After passing the outer marker, the aircraft descended below the glide slope, entered an area of heavy rain, was struck by lightning, and crashed.

“There was no in-flight damage to, or malfunction of, the aircraft’s structure, powerplants, or systems. There was no evidence that lightning caused any malfunction of essential systems or caused structural damage.

“The National Transportation Safety Board determines that the probable cause of the accident was the aircraft’s encounter with a downdraft following the captain’s decision to initiate and continue an instrument approach into a thunderstorm. The captain’s decision probably was influenced by the lack of a timely issuance of a severe weather warning by the National Weather Service, and the improper assessment of the weather conditions in the terminal area by the flightcrew and the flight dispatcher.

“As a result of the accident, the National Transportation Safety Board made six recommendations to the Federal Aviation Administration.” (NTSB 1974, 1)

“History of the Flight

“Ozark Air Lines Flight 809, an FH-227B (N4215), was a regularly scheduled passenger flight between Nashville, Tennessee, and St. Louis, Missouri. It made scheduled stops at Clarksville, Tennessee, Paducah, Kentucky, Cape Girardeau, Missouri, and Marion, Illinois.

“The flight departed Marion, Illinois, at 1705 on July 23, 1973, with an instrument flight rules (IFR) flight plan to Lambert-St. Louis International Airport. Forty-one passengers and three crewmembers were on board. The flight proceeded via the V-335 airway toward St. Louis without difficulty. The flight was under the radar surveillance and control of the Kansas City Air Route Traffic Control Center (KCC).

“At 1726:47.7, the KCC controller requested that Flight 809 make a 360 [degree] turn to the right. He advised that there would be about a 5-minute delay and that the right turn would keep the flight clear of the weather. The flightcrew indicated that they would comply with the request.

“The cockpit voice recorder (CVR) tape indicates that immediately after the controller’s request, the first officer said, “We’re not going to be able to make it. I don’t know, unless we follow it inbound.” After the captain replied “Okay,” the first officer asked “That’s Okay?” The captain said “Yeah.” The first officer said, “It’ s about 30 miles then from us, between us and the outer marker.” The captain replied, “About over the outer marker,” to which the first officer responded,, “That’s right.”

“At 1728:52.3, the KCC controller cleared the flight to proceed to the St. Louis VOR and to contact St. Louis Approach Control . At 1729:47, the first officer transmitted, “Approach, this is Ozark eight oh nine, seven thousand, with Quebec” The pertinent information in the Quebec broadcast was: Estimated ceiling 4,000 feet broken, visibility – 5 miles, haze and smoke, wind-120° at 8 knots, temperature 92°, altimeter 30.06. ILS runway 12R approaches in use, landing and departing runways 12. The approach controller respond: “Ozark eight oh nine, Roger, maintain seven thousand and, . . . continue toward the VOR…vectors runway three zero left ILS.” The first officer acknowledged with “Roger.”

“The first officer then called Ozark operations personnel on the company radio frequency and reported that the right engine fuel boost pump and the main inverter were inoperative. Then he called the Spirit of St. Louis Airport Unicom and asked the operator to inform a local general aviation company that he would be 15 or 20 minutes late.

“Between 1732:26 and 1739:22. the approach controller gave Flight 809 radar vectors through an area of thunderstorm cells that lay south and southeast o f the St. Louis Airport. A t 1740:12.9, the controller cleared the flight for an ILS approach to runway 30L. A t 1740:42.6, he cleared the flightcrew to contact the St. Louis Control Tower and informed them that the flight was 2 miles from Berkley….

“At 1741:04.3, Flight 809 established communications with the St. Louis tower local controller. At 1742:00.9, the controller said, ‘…Ozark eight oh nine, you’re in sight and cleared to land runway three zero left.. .’ The first officer acknowledged the clearance and asked for wind information. The controller responded: “Wind is, it ‘ s been gusting, … it ‘ s right now, it’s two- two-zero. I t ‘ s been around to about three four zero degrees, holding at twenty but occasional gust up to thirty-five.” The first officer replied, “Roger.”

“At 1742:31, the local controller said, “Ozark eight oh nine, it looks like a heavy rain shower moving right across the approach end of the runway now.” The first officer replied, “Roger, we see it.” That was the last transmission from the flight. The CVR stopped a t 1743:24.

“The local controller stated that he lost sight of the aircraft because of the rain. Until that time, he had observed Flight 809 executing what appeared to be a normal ILS approach. He continued to follow the flight’s progress on the tower radar, but lost primary radar contact when the flight was about 2 miles from the runway. When he observed the alpha-numeric radar track of the aircraft move to the left of the localizer course, he tried unsuccessfully to make radio contact with the flight.

“Flight 809 crashed into a residential area about 2.3 miles southeast of the approach end of runway 30L and about 700 feet south of the extended runway center line.

“An aeronautically qualified witness, who was about 2,000 feet north-northwest of the accident site, stated that he had observed the aircraft executing what appeared to be a normal ILS approach. As the aircraft continued the approach, it suddenly ascended about 400 to 500 feet and
then rapidly descended to 200 feet above the ground. Shortly thereafter, according to the witness, lightning struck the wing just outboard of the left engine. The lightning was followed by a rolling flash of fire. The aircraft again lost altitude and, after several apparent “evasive maneuvers,” disappeared into the rain and trees.”

“Other witnesses, who were east-southeast of the accident site and at various points along the flightpath of Flight 809, reported that the aircraft’s altitude had appeared ‘much lower than normal.’ They stated that it had been raining heavily and that the wind had been blowing very hard from the southwest. One witness, who was about 1.4 miles east-southeast of the accident site, said that the aircraft had flown low over her house and had disappeared into an area of heavy rain west-northwest of her position….

“A light twin-engine aircraft that preceded Flight 244 on the same ILS approach landed on runway 30L at 1740. The pilot stated that he had difficulty controlling his aircraft after intercepting the localizer course about 4 miles southeast of the outer marker (OM). Because of a
strong updraft, he was unable to descend from 6,000 feet mean sea level (m.s.1.). A downdraft near the OM caused his aircraft t o drop 3,500 feet per minute, the maximum rate displayed on the instantaneous vertical velocity indicator. He flew the aircraft out o f the downdraft near glidepath altitude several miles from the end of the runway, continued the approach, and landed. Several minutes later, a dark, heavy rainstorm, with strong, gusty surface winds, moved across the airport from the west and northwest….” (NTSB 1974, 2-4)

“Trees surrounding the accident site were damaged by wind. The heaviest damage was in an area which extended from a short distance northwest to about 1 mile southeast of the accident site and approximately ½ mile on both sides of the localizer course. A NWS expert estimated that winds of 65-70 mph would have been required to cause such damage.” (NTSB 1974, 9)

“The Ozark Air Lines Operations Manual contained procedures for thunderstorm recognition and avoidance. The company’s general policy was to suspend operations over a route or a particular area if thunderstorms generated an unacceptable level of turbulence. Also, the company advised against penetrating any known thunderstorm cell which had been detected visually or by airborne weather radar. The avoidance criteria specified were: (1) The pilot should attempt to avoid thunderstorms which are suspected to be severe, by 20 miles a t a11 levels, and (2) he should attempt t o avoid all other thunderstorms by 10 miles at all levels.

“With reference to operations into terminals with high-density traffic, the manual cautioned pilots as follows: “. . . little space is available to permit deviations; therefore, you must evaluate the weather situation in the terminal area well prior to arrival and inform ATC of your intentions so that the area and approach controllers can take appropriate action to avoid conflict”.” (NTSB 1974, 16) ….

“Analysis ….

“The flight was routine until it approached the St. Louis terminal area. At that time, the flightcrew was aware that thunderstorms which existed near the airport might block the flight’s approach.” (NTSB 1974, 18)

“”Approach Analysis – The Board attempted to determine why a qualified air carrier pilot would continue an approach into severe thunderstorm conditions when alternate courses of action were available to him. Because of the crew’s lack of recollection of the events that preceded the accident, it is necessary to hypothesize regarding those factors that might have affected the captain’s decision. The factors considered by the Board included: (1) Company pressure to adhere to published flight schedules, (2) company training regarding recognition and avoidance of thunderstorms and associated severe weather phenomena, (3) available weather information, and (4) assessment by the captain of the available weather information.” (NTSB 1974, 19) ….

“An experienced pilot should have been aware of the updraft and downdraft hazards associated with roll clouds that precede thunderstorm activity. These clouds are a direct indication of the extreme severity of the associated thunderstorm activity, and they should be avoided by a substantial distance.

“Additionally, the surface wind information and the heavy rain observation provided by the local controller should have alerted the captain that he was continuing his approach into difficult conditions. He was faced with landing the aircraft i n heavy rain on a wet runway in a strong crosswind.

“Considering these factors, the Board believes there were sufficient cues available to the captain to alert him to the possibility of turbulence, downdrafts, and limited visibility if he continued the approach through the rain area on the final approach. Because he could see the runway through the rain the captain continued the approach into the area of severe downdrafts and restricted visibility. Had the captain been better informed regarding the hazards associated with low-level turbulence in thunderstorms, his decision might have been to execute a missed approach and hold until the weather improved or to divert to an alternate airport….

“Weather Analysis — The captain derived virtually all his information about the location and severity of the thunderstorm activity from visual observations and the airborne weather radar. The area and terminal aviation weather forecasts did not provide significant information about the location or severity of the storms.” (NTSB 1974, 20) ….

“As a result of this and several other accidents which have occurred during thunderstorms in terminal areas, the question arises whether FAA controllers should be authorized to refuse pilots’ requests for an approach, landing, or takeoff, when the weather conditions at the airport are too severe, in the controller’s opinion, for safe terminal area operations….

“Survivability — The accident was nonsurvivable with respect to the passengers because the decelerative forces approached the limits of human tolerance, the restraint mechanisms failed, and the occupiable area did not remain intact. The fatal and nonfatal injuries alike indicated that the decelerative forces had been near the limits of human tolerance. All but one of the passenger seats failed during the crash sequence. The passenger cabin was torn open by impact with trees, and the unrestrained occupants were ejected with sufficient force to produce fatal injuries upon collision with unyielding objects. Four passengers survived because they were thrown clear, without colliding with any objects that could inflict more serious injuries.” (NTSB 1974, 21)

“Both pilots survived because the cockpit remained relatively intact and their restraint mechanisms (seats and seatbelts) did not fail Significantly, both pilots probably would have received only minor injuries, had their upper torsos been restrained by shoulder harnesses.” (NTSB 1974, 22)

Sources

Kimura, Chris Y. World Commercial Aircraft Accidents 3rd Edition, 1946-1993, Volume 1: Jet and Turboprop Aircrafts. Livermore, CA: Lawrence Livermore National Laboratory, Risk Assessment and Nuclear Engineering Group. 4-11-1994.

National Transportation Safety Board. Aircraft Accident Report. Ozark Air Lines, Inc. Fairchild Hiller FH-227B, N4215 Near the Lambert-St. Louis International Airport, St. Louis, Missouri, July 23, 1973 (NTSB-AAR-74-5). Washington, DC: NTSB, April 24, 1974, 43 pp. At: http://libraryonline.erau.edu/online-full-text/ntsb/aircraft-accident-reports/AAR74-05.pdf