Failure Knowledge Database / 100 Selected Cases

Crash of American Airlines Boeing[December 29, 1995, mountainous terrain near the Cali Airport, Colombia]
Masayuki Nakao
Institute of Engineering Innovation, School of Engineering, the University of Tokyo

When a crewmember of American Airlines Flight 695 changed an approach course
to an airport in order to recover from a delay in the schedule, he input only “R”
instead of “ROZO” in the computer. The computer interpreted it as an input cord of"ROMEO" of Bogotá, Columbia beginning with "R" in the same way. The crew
entrusted the computer to make a course change without noticing the mistake. Theairplane swerved off the original course and crashed into mountainous terrain nearCali, Columbia. 159 out of 163 crew and passengers died.
1. Event
On December 20, 1995 at about 9:45 p.m. (US Eastern Standard Time), American
Airlines Boeing 757 (figure 1), flight 965, from Miami, Florida to Cali, Colombia hit
the west slope of a mountain at about 8,900 feet Near Cali and crashed into the Westslope near the peak of the mountain. In this accident, 159 people died and 4 people
were seriously injured. Among the 163 in total were 2 flight crews, 6 flight attendants
and 155 passengers.

Figure 1. Boeing 757 Model
2. Course
On December 20, 1995, airplanes of Miami airport arrival services from thenortheast district were behind schedule due to bad winter weather in the Northeast ofAmerica. American Airlines Boeing 757-223 (N651AA) flight 965 waited at Miami
Airport for transit passengers from the Northeast region.
The plane left Miami Airport at 18:35 (US Eastern Standard Time), two hours

1Failure Knowledge Database / 100 Selected Cases

behind schedule, and was scheduled to arrive at Cali Airport about 21:45.
At about 19:36, the controller advised the flight crew to take the shortest approach
route (ROZO One approach route) to Cali for landing. Flight 695 was traveling twohours behind schedule and the crew decided to change its route to the shortest
approach route at about 19:37 to recover some of the delay.
The normal approach route to Cali flies the plane from Tulua VOR (note 1), about
57km north of Cali (Alfonso Bonilla Aragon) Airport, towards Cali VOR, about 14km
south of Cali Airport, and lands it at Cali Airport by curling North, however, it could
alternate to pass ROZO VOR about 17km north of the Cali Airport and directly land
at Cali Airport from Tulua VOR by the ROZO One approach route. Flight 695 decided
to take the ROZO One approach route from Tulua VOR, but decided to go directly toROZO VOR because it had already passed Tulua VOR. In the course of changing theroute, a crewmember input “R”, for ROZO VOR (ROZO), which was a waypoint of theroute after the change, into the FMS (a flight control unit). Then flight 695 deviated toleft from the course and was lost in the Andes. The captain who noticed that thecourse deviated to the left told the copilot to turn right, but the plane had alreadystrayed into the mountainous terrain and GPWS (note 2) began to sound about 1
minute later. The sound of GPWS upset the crew who tried to gain elevation without
closing the flight flaps that were activated for a nosedive landing. Although the crew
increased the engine power to maximum, the plane crashed while grazing themountaintop without rising (cf. figure 2).
Radio communication was lost after the crew last requested the Cali Airport forlanding approach.
The plane crashed in near the mountaintop 33 miles northeast from Cali VOR. It
was 10 miles away from the usual course, and at an altitude of 8,900 feet (altitude ofCali is 3,153 feet).
Eyewitness residing in the mountainous terrain described the accident “Theairplane collided with the hillside and went up in huge flames.”

Figure 2.

the planned course and actual course of AA Flight 6952

Failure Knowledge Database / 100 Selected Cases

Note 1)

VOR (VHF Omni-directional Range)
The VOR station sends a signal of frequency 108.0 to 117.95 MHz, anda plane can determine the correct course from the VOR station in a
resolution of one-degree.

Note 2)

GPWS (Ground Proximity Warning System)
If a plane, or a helicopter appears headed for impact into the ground orstructure, it gives an alert signal that for the human sight and hearing.
With a database of all topography and structures in the world, it works
based on a flight course in conjunction with sensors and GPS.

3. Cause
When a crewmember changed the approach course to the airport to regain adelay in schedule, he input only “R” instead of “ROZO on a computer.
The FMS misjudged the R with instruction to go to the capital Bogotá that had
higher frequency of use than that of ROZO (FMS was programmed to choose acourse of higher frequency of use when there were other way points that had thesame initial nearby).
Because the crew completely depended the course change on the computer
without noticing the choice of FMS and did not attempt to grasp the position bythemselves, the airplane continued its descent. Due to the steep topography of theAndes around Cali, when the airplane missed the proper course and turned, itcrashed into the mountains in the suburbs of Cali.
Honeywell Air Transport Systems Co. delivered the flight system of the plane,and Jeppesen Sanderson Co. was in charge of the software. 11 months before theaccident, an internal memo of Jeppesen was discovered, "It could cause a large
incident if these problems in the flight support system are left unresolved. They
must meet customer needs by all means, now.”
According to the record of Jeppesen, 95 out of 8,000 radio signal lamps
worldwide were not registered in the database, and the ROZO with low frequency
was recorded in a different file in the computer.
Meanwhile, during a further lawsuit, American Airlines sued both Jeppesen andHoneywell claiming they were partially responsible for the compensation anddamages paid to victims because of the problem with the computer on the plane.
The final judgment held American Airlines 75% responsible, Honeywell 17%, andJeppesen 8%.
4. Immediate Action
Immediately after the accident, people were urgently dispatched from American
Airlines, the Federal Traffic Safety Board (FTSB), Federal Aviation Administration

3Failure Knowledge Database / 100 Selected Cases(FAA), and Boeing the plane manufacturer.
5. Summary
This case is an example of a computer software specification intended for better
human interface turning around and causing an accident. The event was a big
wake up call not to put too much confidence in the computer for the modern societythat is starting to fully immerse itself into the computerized society.
6. Knowledge(1) People can fall into a pitfall if they try a shortcut without confirming thesituation.
(2) A program may lack safety if it is made only for convenience.
(3) Human knowledge and concentration should provide safety instead of relying
solely on the computer.
(4) An unexpected danger hides behind changing the usual routine.
7. Background
The accident airplane, Boeing-757, was a so-called "glass cockpit" type, which
was the first commercial plane with autopilot. The "glass cockpit" has CRT andLCD displays for its instrumentation instead of analog meters.
This type of airplanes carries a computer called FMS, whose monitor displays
navigation data, system monitors, and the flight route. FMS automatically steers
the plane to the aimed route when a pilot inputs the route into the CDU from theconsole; it was a breakthrough airplane required only two pilots (operable fromeither seat) to fly.

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