British Airways B772 at London on Jun 11th 2021, rejected takeoff due to unreliable speeds
Last Update: January 28, 2022 / 19:13:43 GMT/Zulu time
A replacement Boeing 777-200 registration G-YMMA reached Accra with a delay of about 5:15 hours.
The AAIB reported the occurrence was rated a serious incident and is being investigated, all three pitot systems provided unreliable air speed indications. In addition, British Airways had two more unreliable air speed events involving an A320-200 with 2 blocked pitot tubes and an A320-200N with one blocked pitot tube in about the same time frame.
The AAIB released their bulletin, handling a number of similiar occurrences between Jun 9th 2021 and Jul 19th 2021 in this report, and concluded:
Over a short period of time, several aircraft suffered air data problems related to the blockage of pitot probes by insect nests.
From an operational perspective, 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. Therefore, even though traffic levels and aircraft utilisation are expected to increase in 2022, the seasonal risk of insects blocking pitot probes could be significant. Proactive habitat management and aircraft monitoring will be required to mitigate the risk. With the move towards ‘greener’ aviation, this may become even more important in the future.
With respect to G-YMMR the AAIB summarized the sequence of events:
Before the incident flight, G-YMMR had been positioned at Heathrow for six days, most of the time in the overspill parking area at Terminal 4, but also on a maintenance stand at the north-eastern area of the airport. In preparation for flight, it was towed to Terminal 5 ahead of its scheduled departure.
The flight crew did not detect any system anomalies until early in the takeoff roll. Just after the PM verbally confirmed that takeoff thrust was set, both pilots looked at their flight displays and saw their airspeed indicators were not reading. The commander made the executive “Stop” call and the aircraft was brought to a halt on the runway without further incident. After reviewing the aircraft status and noting that the brake temperatures were not excessively high, the flight crew taxied the aircraft back to the terminal.
Inspection of the aircraft pitot probes showed that both the right and centre probes were blocked. The nature of this debris (Figure 3) was similar to that found on G-EUUO and G-TTNH. However, with the aircraft having been parked at a different location to the other two aircraft, the operator now considered that this was a wider issue, and the event was notified to the AAIB and the aircraft quarantined for inspection.
As two of G-YMMR’s probes had been found to be blocked (right and centre), all three probes were removed. The Total Air Temperature probes and static ports were inspected and found to be clear. The pitot/static system was flushed, and new probes fitted at the left, centre and right locations. No further debris was found during the system flushes. No previous reports of pitot/static system or ASI system defects had been reported on the aircraft and, following testing, it was released back to service.
This article is published under license from Avherald.com. © of text by Avherald.com.
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