Since the beginning of 2020, Airbus has received an increasing number of reports of unreliable airspeed events at takeoff due to Pitot probe obstruction. Despite the existing prevention means and the preflight exterior walkaround, takeoffs with obstructed air data probes may happen. This article highlights why it is so important for pilots to actively monitor the airspeed during the entire takeoff roll, to detect an airspeed discrepancy as early as possible, and safely reject the takeoff, if required to do so.
MULTIPLE UNRELIABLE AIRSPEED EVENTS AT TAKEOFF
Preparing for a Safe Return to the Skies is a Safety first article published in June 2020 that already highlighted the increased risk of unreliable airspeed events after aircraft parking or storage. The number of reported occurrences since this article was published is still a reason for concern.
Between January 2020 and March 2021, 55 events of unreliable airspeed indication during takeoff were reported to Airbus.
Majority of events linked to Pitot obstruction
44 of the 55 reported cases of unreliable airspeed at takeoff were due to obstruction of the Pitot tube. Obstructions can be caused by the presence of insects, sand, dirt, dust or any other foreign materials that could enter the Pitot when protective covers are not fitted to the aircraft when on the ground. In one reported case, the obstruction was because the protective covers were not removed before the flight.
Pitot contamination occurring during various types of parking conditions
The chart below (fig.1) shows the duration of time an aircraft spent on the ground before the flight when the unreliable airspeed event occurred.
(fig.1) Duration of time an aircraft spent on ground before reported unreliable airspeed event
Also beware during shorter ground stays
Contamination of Pitot probes by insects does not happen only during long periods of parking or storage. Half of all reported Pitot contamination related events occurs when the aircraft is parked for a time period of less than 48 hours. A significant number of reported occurrences of obstructed Pitots were on aircraft in transit and on the ground for less than two hours. Pitot probes are not always protected by covers during short duration transits.
Why Pitots are even more exposed to the risk of contamination during the pandemic
The COVID-19 pandemic had the effect of a significantly reduced number of flights, which means aircraft spent more time on the ground between flights. In cases where the air data probe protective covers are not fitted, the exposure to the risk of Pitot contamination is greatly increased.
Source – Airbus Safety Magazine
