Varig Flight 254: Downed by a decimal point

# Introduction

Varig flight 254 was a Boeing 737-200 which made a forced landing in the Amazon jungle after running out of fuel on 3 September 1989, 600 miles off course. The aircraft was mechanically sound and the pilots were fit to fly. The main cause of this accident was the crew entering a wrong heading into the aircraft’s flight computer. The aircraft was downed by a misplaced decimal point.

Image embedded from Air Disaster.com on 19 August, 2010.

# Initial error

The first active error in this accident was committed while the plane was still on the ground at Marabá airport. The Captain looked at the flight plan and saw that the required magnetic heading to get to Belém was 0270 degrees. The Captain thought this meant 0270. degrees, when in fact it was 027.0 or 27 degrees. This was due to the airline’s procedure of implying the decimal point was always placed to the left of the last digit. Having completed this task six times during the day's flights, he was likely complacent and not concentrating on the relatively simple task of reading a number correctly. When the Captain looked at the heading, he likely forgot about the implied decimal point to the left of the last digit, and read 0270 degrees as a normal number, with the implied decimal point to the right of the last digit. As a consequence, the captain entered 270 degrees into his HSI. He also entered the distance to Belém, 187 nm, into the aircraft’s flight computer.

## Latent error

While it was the pilots that entered the incorrect heading, it was a latent error that enable the active error to take place. Varig's flight plan was designed counter-intuitively, and created the potential for pilots to miss-read the heading. After the accident, Varig changed the flight plan layout and solved this latent error.

## Failure to cross-check

The second error was committed by the First Officer. After returning from examining the exterior of the aircraft, he copied the magnetic heading of 270 degrees from the Captain’s HSI, and entered into his own. It is standard procedure for the FO to read the heading from the flight plan himself, rather than to copy it from the Captain’s HSI. If he had done this, the error may have been detected. Disregarding standard procedures is an example of a hazardous anti-authority attitude.

# Lack of situational awareness

After take-off the aircraft began a large turn to the left, and aligned with 270 degrees, which instead of heading to Belém, headed out over the Amazon jungle. The pilots obviously did not have enough situational awareness to realise they were heading in the wrong direction. This may be due to a third active error being committed. There are suggestions that the flight crew was listening to Brazil vs. Chile World Cup match in the radio1, another example of a hazardous attitude.

# Weak VHF radio signal

When the pilots thought they were approaching Belém, they tried to contact Belém tower on their VHF radio. They failed to make readable contact as they were out of range, but managed to relay information via another aircraft. At this point, the weak VHF signal should have alerted the pilots to the fact that they were not close to Belém. After receiving a clearance to descend to land, the crew became confused as they could not locate any familiar landmarks. The combination of a setting sun and haze would have reduced visibility significantly. As Belém airport was not equipped with radar, the controller did not know that the aircraft was actually miles away over the Amazon.

# Atempt to rectify situation

The aircraft’s flight computer then started showing that the aircraft had overshot its destination of 187 nm at a heading of 270 degrees magnetic. As a consequence, the pilots began a 180 degree turn, descended to 4,000 feet, slowed to 200 knots, and attempted to visually locate Belém, still believing they were in the right location. After failing to locate Belém, the pilots did not tune into any navigational aids, instead attempting to locate their position by following an incorrectly-identified river for over thirty minutes, the fourth error.

## Confirmation Bias

At this point, the crew was likely under the influence of confirmation bias. This means that any new information was biased towards supporting their hypothesis that they were flying from Marabá to Belém. There were three points where they should have realised their situation. Upon receiving the weak VHF signal, upon failing to locate familiar landmarks, and upon overshooting Belém. The pilots possibly had an 'invulnerable' attitude, not believing they were truly lost until it was too late. Confirmation bias was likely for four reasons:

-High expectancy
The pilots had read the heading from the flight plane, inputted it into the aircraft’s flight computer, and arrived at their destination many times. As a consequence, there was an understandably high expectancy that this time would be no different.

-Diverted attention
If the pilots were listening to a soccer match on the radio, their attention was surely diverted from flying the aircraft and monitoring their situation.

-Defence against bad news
To realise they were 600 miles off track in the middle of the Amazon would be bad news indeed. Therefore, the pilots were likely to not believe this was the case until overwhelming evidence pointed towards it.

-After concentration
The pilots had already flown six routes that day, require effort and attention. On the last route, they were likely to be relaxed and careless.

# Tuning incorrect radio beacons

The pilots then realised the incorrect magnetic heading. The FO managed to tune into two radio beacons, believing they were Marabá and Carajás. In fact, instead of tuning into Marabá, he had committed the fifth error and tuned to the Goiânia beacon, which was actually 675 nm away, the signal being reflected of the Ionosphere. The Carajás beacon was not even operating, instead he tuned into the Barra do Herons beacon. The pilots were too preoccupied with locating their position to notice the incorrect Morse code identifiers, a sixth error. This was likely due to expectation or mind set, where by the brain hears (or sees) what it expects to hear.

# Crash landing

The 737 actually passed within 100 nm of an Air Force base, where they could have comfortably landed. By now the sun had set, and the pilots realised they would soon run out of fuel. After using all of their fuel to prevent a post-impact fire, the pilots crash landed the aircraft in the jungle. The wreckage was located two days later, there were thirteen fatalities and fifty-four survivors.

References
1. THE 737 TECHNICAL SITE. (1999). The complete Boeing 737 write-off listing. Retrieved 19 August, 2010 from: http://www.b737.org.uk/accident_reports.htm.
2. AVIATION SAFETY NETWORK. (n.d.). Accident description. Retrieved 19 August, 2010 from: http://aviation-safety.net/database/record.php?id=19890903-0
3. WIKIPEDIA. (2010). Varig flight 254. Retrieved 19 August, 2010 from: http://en.wikipedia.org/wiki/Varig_Flight_254.