How A Wasp Nest Caused One of the Worst Aviation Disasters

• An air disaster is thought to have been caused by a wasp nest blocking a vital speed sensor.
• The problem persists to this day, and has led to multiple close calls.
• Researchers are working on solutions to keep aircraft and their passengers safe.

The desperation was clear in the pilot's last recorded words. "Don't pull back, please don't pull back [...] oh what's happening?"

Twelve seconds later the recording went dead. It was February 6, 1996, and Birgenair Flight 301 had crashed into the sea, killing all 189 people on board.

So what happened? The investigation was complex, and found that the cause, first and foremost, was pilot error. But the start of the sequence of events that led to the tragedy was eventually traced back to something relatively innocuous: a wasp nest.

It was suspected that a nest had blocked a vital sensor, confusing the pilots, who failed to heed warnings that might have saved the aircraft.

It may sound far-fetched, but the problem still exists today. Across the world, researchers in several fields are grappling with how to stop wasps from causing delays and, in extreme cases like that of Flight 301, disaster.

As airports strive to become greener for environmental reasons, and climate change drives species into new areas, the problem has only become more pressing—but there are promising solutions, some of them ingeniously complex, others disarmingly simple.

What Happened on Birgenair Flight 301

The disaster that focused minds on the issue was that of Birgenair Flight 301. It was scheduled to fly from Puerto Plata in the Dominican Republic to Frankfurt, Germany. Most of the passengers on board were German tourists returning from vacations in the Caribbean.

As the aircraft was beginning its take-off, the captain of the Boeing 757 noticed that his airspeed indicator was not working, but proceeded as planned. That was the crew's first error, according to Geoff Dell, a safety scientist and professor at the Technical University of Ostrava who specializes in systems safety, risk management, and human factors engineering.

"The take-off should have been terminated and the reason for the misreading airspeed indicator investigated," he told Newsweek.

Soon after take-off, the "stick shake stall alert" was triggered, shaking the pilots' controls to warn them the aircraft was flying dangerously slowly. The autopilot disengaged and the aircraft began to veer off course and travel downwards.

It wasn't long before the plane crashed into the Atlantic Ocean. Everyone on board—176 passengers and 13 crew members—was killed instantly.

An investigation concluded that one of the aircraft's three pitot tubes—pressure sensors that stick out from the fuselage and are used to measure the aircraft's airspeed—was blocked. This would have caused the crew to receive incorrect airspeed information.

It is not 100 percent certain what caused the blockage, but the most likely suspect was a wasp nest.

How to Stop Wasps

The black and yellow mud dauber is a well-known wasp to pilots in the Dominican Republic. The wasps are prone to building their nests in artificial, cylinder-type structures, like pitot tubes. Even though no pitot tubes were recovered, the Birgenair jet had not flown in 20 days before the crash took place. This would have been more than enough time for the wasps to create their nest, which led to the strong suspicion one was to blame.

While the Birgenair crash was an extreme example, the problem is widespread. In June and July 2021, eight aircraft at London's Heathrow Airport were found to have pitot tubes blocked by insects, eggs or nest debris.

"The drive to greener aviation and urban environments will result in quieter, cleaner aircraft and less polluting airports, providing the kind of environments that prove attractive to insects such as bees and wasps," the U.K. Air Accidents Investigation Branch said in a report, although it added that the problem was exacerbated by the amount of time aircraft had been grounded during the COVID-19 pandemic.

Brisbane Airport, in Australia, has had similar problems. Keyhole wasps, a species also now found in the southern U.S., were found to have been blocking pitot tubes and in 2013 an Airbus A330 was forced to turn back shortly after take-off due to a malfunction in the captain's airspeed indicator.

A study by consulting firms Ecosure and Eco Logical Australia, published in the journal PLOS One, examined the issue, placing probes in replica pitot tubes at the airport between February 2016 and April 2019. It found that 93 were blocked in that period, all by keyhole wasp nests. The species "poses a significant risk to aviation safety," the study said.

There were two solutions. The first was simply to cover pitot tubes when aircraft arrive at Brisbane Airport. However, this carries its own risks. On July 18, 2018, an Airbus carrying 229 people took off with the covers still in place on its pitot tubes. It climbed to 11,000 feet, before being forced to turn back. The solution had caused exactly the kind of problem it was intended to prevent.

The airport is also using another preventive measure. This is an insecticide based on a South American plant that kills caterpillars that the wasps rely on, which the airport said reduced the number of wasp nests by 64 per cent. After finding a suitable nesting site, female keyhole wasps paralyze several caterpillars and place them in the site, before sealing it with mud. After hatching, the offspring eat the paralyzed caterpillars. Preventing this process can solve the problem at source.

There has also been research into redesigning pitot tubes to make them less vulnerable to wasps and icing, or by replacing them entirely with laser sensors to measure airspeed, the first of which was developed by BAE Systems in 2016.

Pilot Training

Despite these advances, pilot training remains the first line of defense. In the case of Birgenair Flight 301, Dell said that, while it is easy to judge in hindsight, the crew made a series of errors.

"From the cockpit voice recorder read-out, it is apparent the first officer was calling the speeds on take-off based on the correct indications from his airspeed indicator and the take-off was effected safely, but the failure in the captain's airspeed indication system started to have a significant impact after take-off when the autopilot was connected and was responding to the signals from the captain's airspeed system," he said.

"It seems apparent the crew was confused by the conflicting readings and their actions became ineffectual, further adding to the confusion."

Dell said that there are two ways airspeed can be provided to the crew on a Boeing 757 aircraft.

One is with air pressure data from a pitot tube, and another from a standby "auxiliary" airspeed indicator. This indicator is designed to provide reliable airspeed information in the event of a malfunction.

Dell said from the recording taken in the cockpit, there was no suggestion of switching to the standby speed indicator at any time.

"It also seems that at no time did the crew try to isolate the problem, other than an ineffectual attempt at resetting some electrical circuit breakers," he said, adding that "they could have disconnected the autopilot and hand flown the aircraft safely based on just the standby airspeed data, yet apparently failed to do so."

Dell noted that the time between the autopilot being engaged and the end of the recording was only 4 minutes and 28 seconds. But he believes the transcript shows a lack of awareness about how to handle the aircraft's systems and procedures.

"Of course it's easy to find fault with 20:20 hindsight. Clearly this crew was confronted with a circumstance beyond their capability, even though the systems' designers anticipated the possibilities, and once confusion set in the outcome was inevitable," he said.

It was a wake-up call for the aviation industry, which prides itself on improving safety. Even a tiny wasp can set in train a series of events that, for Birgenair Flight 301, would prove devastating for a sophisticated modern airliner—with tragic results for those on board.