When Wasps take fancy to the aircraft Pitot Probe to build mud nests, safety is compromised. – mindFly Katha
Wasps and other foreign objects blocking the Pitot Probes have caused aircraft accident, compromised aviation safety. The aircraft instruments that are affected in most of the events are related to air speed which is vital for takeoffs. The cognitive load of the crew increases since there is a need for analysis at critical stages of flight when there is no obvious fault displayed by the fault handling mechanism.
Between 9 June 2021 and 19 July 2021, several aircraft suffered from abnormal pitot/static system events, two of which resulted in rejected takeoffs. The U.K. AAIB investigation identified the cause to be the nesting activity of certain species of wasps and bees within pitot probes.
Interactions between aircraft and wildlife are frequent and can have serious financial and safety consequences. Birds are the most common threat to aircraft , with a host of terrestrial animals also implicated . There were over 16,500 reported incidents involving birds and a further 397 involving other vertebrates at Australian airfields between 2008 and 2017. The majority of these incidents occurred during take-off (23.45%) or landing (34.24%), the two most vulnerable phases of flight.
Pitot block accident
In February 1996 a Boeing 757 crashed shortly after take-off from the Dominican Republic, killing all 189 passengers and crew. Anomalous airspeed readings from the pitot probes were responsible for the pilots misjudging the aircraft’s speed. A sphecid (mud-dauber) wasp was believed to have made a nest in one of the pitot probes, although none were recovered. The plane had been standing at Gregorio Lupero´n International Airport in Puerto Plata, and for the two days prior to the fateful flight the pitot probes were not covered as recommended by the manufacturer .
Pitot blockages by aircraft type, February 2016-April 2019 at Brisbane Airport.
The Experiment
An experiment was designed to determine the species responsible, the types of aircraft most affected, the seasonal pattern of potential risk and the spatial distribution of risk on the airport. A series of replica pitot probes were constructed using 3D-printing technology, representing aircraft with high numbers of movements (landings and take-offs), and mounted at four locations at the airport. Probes were monitored for 39 months. Probes blocked by mud nesting wasps were retrieved and incubated in mesh bags. Emerging wasps were identified to species. Results show that all nests in probes were made by P. nasidens, and peak nesting occurs in the summer months. Nesting success (as proportion of nests with live adult emergents) was optimal between 24 and 31˚C and that probes with apertures of more than 3 mm diameter are preferred. Not all areas on the airport are affected equally, with the majority of nests constructed in one area. The proportion of grassed areas within 1000 m of probes was a significant predictor of nesting, and probe volume may determine the sex of emerging wasps.
Nesting success
There were 93 occurrences of blocked pitot probes. Of these, 37 (39.8%) produced live adult wasps, 18 (19.4%) had developed but unhatched wasp imagos, and 38 (40.9%) had contents that were either undeveloped or parasitised. All adult mud-nesting wasps that emerged from pitot probes were P. nasidens.
There is no consistent trend in successful nesting (i.e. completed nests and live hatching) with time of year (Fig 4), and no significant relationship between hatching and rainfall during nesting (F1,37 = 0.010, P >> 0.05): however, rainfall during the previous 3 months and nesting success was positively related (F1,37 = 7.998, P < 0.01). Similarly, mean maximum temperature during nest development and ultimate nesting success were not related (F1,37 = 0.409, P > 0.05). Probes blocked during the peak of summer temperatures and rainfall (January- March: man max. temp. over 3 years 29.6˚C) had lower success rates, nests completed late in the nesting season (April-June: mean max. temp. 24.1˚C) had a greater likelihood of successful emergence and probes blocked after mid-May-October (mean max. temp. 23.4˚C) developed to the adult stage but did not hatch. Incubation times varied greatly, from 16 to 138 days with an average of 45. In the 2016–17 and 2017–18 summer nesting periods, nests that were completed at the start and the end of these periods appear to mature more quickly.
Heathrow incidents
The incidents at Heathrow took place between 9 June-19 July 2021. They were though to be COVID19 related. Aircraft coming out of storage and rusty pilots. Yes there were surprises but looking at the temperature and the other environmental parameters, the condition was perfect for the Wasps to be at their peak of activities.
The UK AAIB report is in the link here.
There were Airspeed indication anomalies and other system related faults triggered during the period. Airbus has issued an OEB but specific to the A-320NEO for airspeed check to be carried out by the crew. An additional verification at 80 kts between the Primary Flight Display and the Standby Instrument, the second is the SOP at 100 kts. Any speed difference of approximately more than 20 kts would call for a reject takeoff.
The report concluded by stating that this threat is not new but was increased during the low activity period of 2021 and is likely to increase in the Spring of 2022.
” Pilot training, preparedness and effective TEM should be considered key elements for assuring early detection of pitot/static system blockages in the takeoff roll, thus minimising the hazards associated with high-speed rejections. As
the airline industry increases its operational tempo toward pre-pandemic levels, operator support for crews balancing commercial pressures against reduced recency will be an important enabler for safely rebuilding operational fluency.
Insects blocking aircraft pitot/static systems is not a new hazard, but one likely exacerbated at Heathrow in 2021 due to the unusually low operational tempo resulting from the Covid-19 pandemic. Reduced traffic levels and human activity resulted in a surge of insect activity during the pandemic lockdowns. With less aircraft activity, including less noise and jet efflux to deter the insects, the parked aircraft made an attractive opportunity, with the pitot probes providing an ideal construction site for nests. The high level of insect activity in 2021 could lead to a larger number of insects emerging in the spring of 2022″.
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