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″.

We have read about the Sharjah incident where the crew took off from the shorter end of the runway. The Captain realised the mistake, gave maximum thrust and selected a higher flap setting. Managed to get airborne safely and an accident was averted. In 2019-20 there have been two incidents in the U.K. where the aircraft has been changed during the day but the documentation change failed leading to the center of gravity issues. The common thread is change management. Is it only for the people sitting in ivory towers or every person involved? It is the safety culture of the organisation or the state which defines the level of commitment of each individual towards upholding the tenets of safety.

The A321 was rolling for takeoff from London, Luton airport when the Pilot Flying (PF) pulled the stick back as is done normally. Nothing happened, the PF pulled the stick further back till it reached the dead end. Still noting happened. The aircraft was accelerating and eating up the runway every second. The Pilot Monitoring (PM) showed presence of mind and pushed the thrust levers full forward to deliver maximum thrust. At this stage when the aircraft is well beyond the decision speed, to have rejected the takeoff too could have been a disaster.

The aircraft got airborne. In the high stress situation, the PM forgot to give the “Positive Climb” call and the landing gear remained down till 5000′ when the crew probably got over the scare and selected the gear UP. Further flight was uneventful.

What happened?

An aircraft change had been made for operational reasons from an Airbus A320 aircraft (A320) to an Airbus A321 aircraft (A321), but no adjustment had been made to the passenger distribution. This led to the passengers being seated towards the front of the aircraft, placing the CG outside the forward limit of the permitted operating envelope.

Passengers were boarded with their seat allocation for the A320 and therefore were seated within cabin Zones A, B and C. This left the seats at the rear of the A321 aircraft, which has a fourth zone, Zone D, unoccupied. The unusual passenger distribution was not noticed by the cabin crew or dispatcher. The aircraft commander was unaware of the passenger
distribution in the cabin but was passed a Load and Trim Sheet for his A321 aircraft, G-WUKG.

Read the full report here.

How did it happen?

On the day of the incident, an A320 was allocated to the flight and this information was passed to Operational Handling Department (OHD) and Passenger Services Department (PSD) at Luton. Both departments received the information and began their respective activities towards producing a Load and Trim Sheet and checking in the passengers for an A320. Later, the OCC needed to change aircraft from the A320 to G-WUKG, an A321. An email informing OHD and PSD of the change was prepared but, due to a technical problem, was not sent. This was noticed later in the day, at 1405 hrs, and the OCC Duty Manager telephoned the OHD and informed them of the aircraft change.

The OHD entered the new aircraft registration into the Load and Trim Sheet software but PSD were not informed and had already allocated passenger seating for the three passenger zones on the original A320. When all the passengers had passed through the boarding gate and taken their allocated seats for the A320, the software produced a Load and Trim
Sheet with passenger distribution for the four zones of the A321, maintaining the CG within limits for the flight.

Change mangament

This is a second incident in less that a year in U.K. where the change management has led to a serious incident. The first one took place between an A320 CEO change to an A320 NEO where both have different certified Operational center of gravity limits. COVID19 prevailing environment and the social distancing was stated to be a contributory cause while the primary cause was a back end failure of the synchronization. The load master would normally present the load and trim sheet . An anomaly or doubt would be discussed with the load master and the issue would be clarified. Due to the social distancing SOP, the cabin attendant passed the details to the crew, thereby eliminating the safety barrier.

At Luton, the change could not be conveyed to the station due to the failure of the email to reach in time. However, this change should have been addressed by other in the system those who act as safety barriers. No one questioned or raised any doubt. The Operations Control Center too assumed that the change would have been addressed but neither confirmed. The error passed on till the crew realised that the aircraft will not leave the earth since the passenger seating it too forward.

Safety Culture

Safety culture reached a generative stage when everyone feels responsible for safety of themselves and that of others. It is everyones responsibility. Therefore training of personnel is vital and ensuring that not just top managers understand and practice safety but everyone does it equally will save future occurrences

 To understand this, we need to define fear. Fear is a subjective in nature and every person will define it a bit differently depending upon the perception. One of the definition is “Fear is the natural, and therefore reasonable, response to danger.” If this definition is correct, fear should then be proportional to the knowledge of the danger, to a realization of the risks involved. Who knows so well as the nurses and doctors the dangers of contagious infections? Is the fireman afraid of the fire or the army man afraid of the sound of a burst of bullets? The infection, fire and bullets are all dangerous. Therefore it can be said that the feat is not proportionate to the the actual risk of injury.

Fear of bombs

When the World War was in full swing and there was a threat of London being bombed. When the sirens were first sounded there was little panic and people scurried to their bomb shelters with little confidence of seeing the daylight again. A number of times when the sirens sounded , no bombs dropped. Soon people bean to be adventurous and came out of the shelters to see what’s happening around and were later joined by more people. 
What was the explanation of this? The intelligent layman would say: “Oh, it’s just a case of Wolf, Wolf”. The psychologists would explain it as the extinction of the conditioned reaction. There are other adages like “Out of site, out of mind”. The ostrich philosophy grew and all caution was disregarded.

Fear groups

Soon the bombs started falling for real. When the bomb exploded in a congested area, it divided the population who can hear it or see its effects into three groups.

1. Those who are killed. The morale of the community depends on the reaction of the survivors, the killed do not matter.The survivors are divided into the near miss and remote miss.
2. The near misses are the people who are in immediate vicinity of the bomb, they feel the blast, they see the destruction and are horrified by the death and carnage. In this category, there are people who think, “The next one will get me” or ” Will the next one get me?”.
3. In contrast, the remote miss group can hear the siren, they hear the enemy plane, explosion. There is tense waiting, will they come nearer? They don’t and the siren for all clear sounds. The survivors think that it has happened and I am safe. Then there is curiosity as what has happened, eager question and speculation. Often there is visit to the scene of destruction. Frequently, the damage is found to be little. In this case the old fear the all bombs will find their mark is dissipated.they don’t get to see the bodies or large scale damage.

As the bombings continued, the people of London became resilient. One English psychiatrist wrote that as bomb sirens were alarmed, “Small boys continued to play all over the pavements, shoppers went on haggling, a policeman directed traffic in majestic boredom and the bicyclists defied death and the traffic laws. No one, as far as I could see, even looked into the sky.
Malcom Gladwell, in “David & Goliath” asks the question, “why we’re Londoners so unfazed by the blitz.” The answer is that when thousands of deaths are spread out across 8 million people, there are far more remote misses than there are near misses and direct hits.

As MacCurdy in “Structure of morale” puts it, “We are also prone to be afraid of being afraid, and the conquering of fear produces exhilaration.” After such events as a bombing are over, “the contrast between the previous apprehension and the present relief and feeling of security promotes a self-confidence that is the very father and mother of courage.”

COVID19 fear

The fear of COVID19 followed similar pattern. When the pandemic was declared, there was fear amongst people that they might contract the infection and meet the fate, that of the people of Wuhan in China. Soon they realized that they do hear about people getting infected and deaths but they haven’t seen it in their vicinity. They began to lower their guards and venture out without taking precautions of wearing the mask properly and/or washing hands. Their confidence grew so much that they began debating on whether to take the vaccination or not. They didn’t realize that every person has the potential to carry and spread the virus and that the vaccination of each and every individual is the only answer. So, if it hasn’t happened to them or people know to them, it need not be feared.
The second wave hit hard since people didn’t take precautions and also refused to get vaccinated. Now every third person is infected with the virus and death is seen very closely. People known to them have died or survived to tell the horrific tales. The fear sets in that they could be next. The situation that they face is the health  infrastructure which was not built to handle a pandemic of this severity is beginning to weather away and there are shortages of essential drugs and oxygen. The vaccination too is in short supply and to ramp up the production it will take time.
MacCurdy writes that the borough that had been panicky and troublesome with its demands for deeper shelter to house the people, after the bombings sticks out its chest and says ” We are on the map now; we can take it”. The same phenomenon is in military. Troops that have never been under fire cannot be relied upon with confidence. But when they have a few casualties they are steadied and, interestingly enough, discipline improves.
It’s always better to be safe than sorry.

A look at the implementation of ICAO safety management system will give a reality check. Only 3 of the 193 member states have reached level 4(fully implemented SSP), 53 are work in progress. What is the status of the remaining 137 states?

Globally, there has been an increase in the number of unstable approaches during the COVID19 period. This is an indicator that despite lower overall air traffic, an unstable approach is still a threat and is not being addressed correctly. It is a decision of the crew, a conscious decision to continue with an unstable approach, is debatable.

The safety data for the first half of 2020 shows that the graph line is riding over the 5-year moving average, which is exceptionally worrying especially since the number of flights has dropped drastically as compared to previous years.

The number of incidents during the COVID times can be visualised from the map below.

The question arises, is the safety management system implemented and effective?

With 117 of 193 member states having initiated level 1 and 3 having implemented level 4, there is a need to evaluate the effectiveness of the safety management system.

With increasing technological development, it is surprising that no developer has come out with an alerting device for an unstable approach. The inference still is a proxy indicator of a risk and not a direct indicator. The crew still needs to derive the risk by monitoring multiple parameters, whereas it can be easily achieved through the use of technology. Systems like ROW/ROPS are a few tools developed for enhancing safety.

mindFly analysis

Unstable approach has been a threat which has been persisting for a long time. A number of measures have been taken to reduce the numbers but still the industry has not been able to reign it in.

A more humanist approach is required to understand the psychology of an unstable approach. Technological barrier is not the answer for every error that a human makes.

The safety management system will not be effective unless the top management has undergone adequate training and show their commitment to the implementation of SMS. A dismal picture of 3 out of 193 member states have fully implemented state safety programmes is extremely alarming.