What happened
On April 12, 1980, at approximately 20:38 local time, a Transbrasil Boeing 727 aircraft, registration PT-TYS, crashed into a hill covered with dense vegetation near Florianópolis, Santa Catarina, Brazil. The flight was operating a scheduled domestic service from São Paulo (SBSP) to Florianópolis (SBFL). All 47 passengers and crew members on board were killed in the accident, although four individuals initially survived the initial impact before succumbing to their injuries or the subsequent fire.
The aircraft had departed normally and climbed through stable air, but encountered significant weather instability during its descent into Florianópolis. The area was under the influence of a strong cold front with heavy cumulonimbus formations, turbulence, and poor visibility. During the descent, the crew requested confirmation from Air Traffic Control (ATC) regarding the operational status of the NDB 280 (FLO) navigation aid, which is used for the DELTA approach procedure. ATC confirmed the beacon was active, and the crew reported receiving the Morse code identification signal.
The aircraft was cleared to descend to Flight Level 050 to begin the approach. However, due to traffic separation requirements with another aircraft at a lower altitude, the descent was delayed. When finally authorized to continue the procedure, the aircraft began its descent. The crew deviated from the intended flight path, likely due to a combination of factors including false locking of the navigation receiver and strong crosswinds. The aircraft impacted the terrain at an altitude of approximately 1,000 feet, striking trees with its left wing before crashing violently.
The investigation
CENIPA (Centro de Investigação e Prevenção de Acidentes Aeronáuticos) conducted a thorough investigation into the accident. Key findings included:
- Weather Conditions: The area was experiencing severe meteorological instability with heavy rain, hail, and turbulence. Satellite imagery confirmed a strong frontal system covering the region.
- Navigation Aid Interference: The NDB 280 signal reception was likely disrupted by electrical interference from nearby thunderstorms. Analysis suggested that the aircraft's Automatic Direction Finder (ADF) may have experienced "false locking" to a distant or reflected signal, causing the crew to believe they were on course when they were not.
- Wind Effects: Meteorological analysis indicated strong winds from the west-northwest (260°–280°) with speeds between 35 and 53 knots. These winds pushed the aircraft significantly off its intended track during the approach.
- Crew Actions: The crew maintained a calm demeanor throughout the incident, as recorded by the Cockpit Voice Recorder (CVR). They did not express concern about their position until very late in the sequence. The descent below safe altitudes was attributed to overconfidence in their perceived location, reinforced by another aircraft having completed the same procedure minutes earlier without issue.
- Aircraft Status: Maintenance records showed the aircraft was airworthy. Weight and balance calculations were within limits. Both flight data recorders (FDR) and CVR were recovered; however, the FDR had limitations in recording vertical acceleration and indicated airspeed during certain phases.
Findings
The probable cause of the accident was a chain of events involving:
- False NDB Lock: Electrical interference from thunderstorms caused the aircraft's navigation receiver to lock onto an incorrect signal, misleading the crew about their position relative to the approach path.
- Strong Crosswinds: Unaccounted-for strong westerly winds displaced the aircraft further east, away from the safe corridor over the ocean and toward the mountainous terrain of Florianópolis.
- Descent Below Minimum Altitude: The crew descended below the minimum safe altitude for the procedure phase, driven by confidence in their navigation instruments despite the adverse weather conditions.
- Turbulence: Severe turbulence made it difficult to maintain precise control during turns, contributing to delays and deviations from the planned trajectory.
Safety action
CENIPA issued several safety recommendations:
1. Crews must exercise extreme caution during descents in adverse weather, strictly adhering to prescribed times, speeds, and altitudes. 2. Florianópolis airport should be equipped with more precise approach aids less susceptible to atmospheric interference, such as an Instrument Landing System (ILS). 3. Further study was recommended on the occurrence of false NDB locking in the region during electrical storms.