The purpose of this article is to provide some insight into a potential danger to aviation, particularly for aircraft operators that fly into tropical and subtropical regions. It is remarkable to think that the instrumentation and safety integrity of enormous commercial airliners can, in fact, be compromised by a tiny insect nest causing a blockage on a small opening on a pitot tube. You will discover how a small, persistent wasp can compromise the safety of a very large aircraft. As you will read, there is a need for further research and mitigation measures to minimize this threat.
I have been a member of bird safety committees at airports in Latin America, and the danger posed by birds who share the skies is clear. Little did I know that this little keyhole wasp, which I have often confronted trying to nest where I was staying in Central America, could in fact be a hidden danger to aviation safety. This article also calls for greater awareness of this threat, from an airport and airline perspective.
Pachodynerus nasidens Latreille 1812 (Keyhole Wasp)
Pachodynerus nasidens, commonly known as the keyhole wasp, is a species of stinging wasp in the family Vespidae. This wasp, native to the Neotropics (including South and Central America and the Caribbean), has been introduced to the northern United States, some Pacific Ocean areas, and Australia.
"While birds and other vertebrates are well known hazards to aviation at airports, the threat posed by invertebrates is less well understood. Here we present an example of a serious risk to flight safety from the mud-nesting keyhole wasp (Pachodynerus nasidens) which views aircraft pitot probes as an attractive nesting opportunity...."[1]
Airlines operating into the Neotropical region including the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone should be familiar with the dangers presented by the nesting behavior of these wasps and the dangers they pose to aviation safety. Walk around procedures should include a greater emphasis on ensuring that the pitot tubes have remained clean and clear of these types of blockages from insects.
Nesting Behavior
This particular wasp has a tendency to use man-made cavities such as keyholes, electrical sockets, and window crevices to construct its nests. It has been introduced to various regions, including the northern United States, some Pacific Ocean areas, and Australia.
"The nesting preference of P. nasidens is for cavities with openings of 6 to 9 mm in diameter (Bequaert 1948; Oliveira-Nascimento and Garófalo 2014), which explains the use of Polistinae cells, which have 6.2 mm in average diameter." [2]
It is a mud-nesting species native to South and Central America and the Caribbean. Known for its adaptable nesting habits, the wasp has raised significant aviation safety concerns in its new environment as it was introduced in Australia relatively recently. For example, a series of incidents have occurred at Brisbane Airport, where vital airspeed measuring pitot probes on aircraft were potentially obstructed by mud-nesting wasps, prompted an urgent assessment of the risks posed by this invasive species. These wasps have discovered a new and unwelcome home, aircraft pitot tubes. These tubes, essential for measuring airspeed, altitude, and vertical speed, are becoming prime real estate for these resourceful insects. The danger increases when the aircraft are parked overnight and allowing sufficient time for the wasps to make a start.
I have personally observed these wasps in Central America starting a nest, and they are quite persistent. I had cleared away the early stages of the nest several times, only to find that they relentlessly returned to finish the job. Knowing the risk they pose to pitot tubes; I was determined to study them and was impressed by how stubborn and tenacious the keyhole wasp is in this regard. It simply refuses to be deterred.
Physical Characteristics
The keyhole wasp (Pachodynerus nasidens Latreille (Vespidae: Eumeninae)) is characterized by its relatively small size and distinctive, dull yellow-brown markings on the distal abdominal segments. These markings are less vibrant compared to those of other species in the same genus, which often have bright yellow markings.
A Pitot tube is a crucial component in aircraft instrumentation, serving as the primary means of measuring airspeed. The first pitot tube was invented by French engineer Henri Pitot in the early 18th century, originally designed to measure the flow of the River Seine!
What is a Pitot Tube?
It's essentially a hollow tube that faces directly into the oncoming airflow. The tube's opening captures the air's total pressure also called stagnation pressure, which is the sum of static pressure (pressure of the surrounding air), and dynamic pressure caused by the air's movement.
How Does it Work?
The oncoming air enters the Pitot tube, causing the air to slow down and come to a complete stop at the tube's end. This creates a pressure buildup known as stagnation pressure. The stagnation pressure is measured by a pressure sensor connected to the Pitot tube. The aircraft's airspeed is calculated by comparing the measured stagnation pressure to the static pressure, which is usually measured by a separate sensor called a static port. The airspeed is then displayed on the aircraft's instruments.
Accurate airspeed measurements help pilots maintain flight paths and altitudes, airspeed data is essential for monitoring aircraft performance and identifying potential issues.
What is a static port?
A static port is another vital component in aircraft instrumentation, working in tandem with the Pitot tube to accurately measure airspeed.
It's simply a small hole or opening on the aircraft's fuselage, typically located on the side or bottom. Unlike the Pitot tube that captures total pressure, the static port measures the static pressure of the surrounding air. This pressure is the pressure the air would have if it wasn't moving.
How it works
As the aircraft flies, the air flows past the static port. The static port is connected to a pressure sensor that measures the static pressure of the surrounding air.
The airspeed is calculated by comparing the measured stagnation pressure from the Pitot tube to the static pressure from the static port.
The difference between these two pressures represents the dynamic pressure, which is directly related to the aircraft's airspeed.
The pitot-static system is the aircraft's vital air data system and allows the aircraft to calculate its speed, altitude, and vertical rate of climb or descent.
Vigilance required when operating in tropical and subtropical regions
For pilots operating in tropical and subtropical regions, where keyhole wasps thrive, a pre-flight inspection is critical. They must carefully check the pitot tubes, ensuring they are free of any obstruction. A tiny wasp nest can lead to inaccurate readings, potentially jeopardizing the safety of the aircraft and everyone onboard.
In 2013, an Airbus A330 was forced to turn back shortly after takeoff due to a faulty airspeed indicator. The culprit? A keyhole wasp nest blocking the pitot tube. "A series of serious safety incidents Brisbane Airport related to the obstruction of vital airspeed measuring pitot probes on aircraft possibly caused by mud-nesting wasps, prompted an assessment of risk." [3]
A study conducted by consulting firms Ecosure and Eco Logical Australia revealed a startling truth: 93 out of 93 replica pitot tubes were blocked by keyhole wasp nests. The study also found that these wasps prefer tubes with larger apertures and are most active in warmer climates, making them a particular threat in tropical and subtropical areas. [4]
The study underscored the need for preventative measures. Airlines are now covering pitot tubes when aircraft arrive in known wasp hotspots. Airports are setting up traps to intercept and capture them to neutralize the treat.
I believe it is important to raise awareness around this particular danger, and that the stakeholders introduce preventive measures, and engage more in collaborative research, to work towards safeguarding our skies from this tiny but tenacious wasp.
Thank you for your attention.
Noel Cox
Principle Aviation Consultant at avcox
References and Citations
1. Alan P.N. House, Jackson G. Ring, Matthew J. Hill, Phillip P. Shaw,
Insects and aviation safety: The case of the keyhole wasp Pachodynerus nasidens (Hymenoptera: Vespidae) in Australia,
Transportation Research Interdisciplinary Perspectives,
Volume 4, 2020, 100096, ISSN 2590-1982, https://doi.org/10.1016/j.trip.2020.100096.
2. Jacques GC, Donizet Ferreira W, Aparecida Moura P, Teofilo-Guedes G, Magalhães de Souza M (2022)
Nesting of the keyhole wasp Pachodynerus nasidens (Latreille, 1812) (Vespidae, Eumeninae) in a nest of a paper wasp
(Vespidae, Polistinae). Journal of Hymenoptera Research 93: 125–130. https://doi.org/10.3897/jhr.93.91298
3. House APN, Ring JG, Shaw PP. Inventive nesting behaviour in the keyhole wasp Pachodynerus nasidens Latreille (Hymenoptera: Vespidae) in Australia, and the risk to aviation safety. PLoS One. 2020 Nov 30;15(11):e0242063. doi: 10.1371/journal.pone.0242063. PMID: 33253188; PMCID: PMC7703898.
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