What happened
On the night of 23 July 2024, a Hawker Beechcraft B200 was being prepared for an aeromedical flight between Gove Airport and Numbulwar Airport in the Northern Territory. Prior to departure, the pilot conducted a pre-flight inspection of the aircraft. A critical step in this process was to remove pitot covers from the pitot tubes[1] on both the front left and right side of the aircraft’s fuselage. These covers protect the pitot tube from contamination and are designed to slide on and off the tubes.
The pitot covers used by the operator were made of tight-fitting rubber to prevent them falling off in the wind. These covers also had a small vent hole in the front which equalised pressure in the pitot system on the ground and facilitated their easy removal. A red streamer is also attached to these covers, which provides a visual reminder to pilots and ground crew that the covers have been fitted and need to be removed prior to departure.
The pilot advised that their usual habit was to tie the pitot cover streamer to the wheel chocks[2] to provide a visual reminder that the pitot covers were to be removed. However, the previous crew had only applied the pitot covers as the aircraft was due to depart later that night and had not set the wheel chocks. Therefore, when the pilot saw that the wheel chocks were not in place, they assumed that the pitot covers had been removed. The pilot advised that due to the shadows created by the floodlights in the hangar they did not notice the pitot cover nor the red streamer during their pre-flight inspection.
The pilot commenced the take-off run and observed normal airspeed indications until the aircraft reached a speed of around 80 KIAS.[3] At that time, the airspeed indications stopped increasing even though the aircraft’s acceleration remained normal and there were no speed warnings in the cockpit. The pilot advised that they cross-checked the indicated airspeed between the primary flight displays (PFD) and the standby instruments, and observed no discrepancy between any of these systems. As a result, the pilot continued the take-off run and the aircraft rotated[4] successfully, albeit with an indicated airspeed lower than normal.
The aircraft climbed to the circuit altitude at Gove, but the pilot noted that the airspeed indicator only showed 100 KIAS even though the aircraft should have been accelerating to 160 KIAS. When the aircraft turned downwind at circuit height, the pilot observed a speed discrepancy in the right PFD and the standby instruments, both of which showed 180 KIAS. This aligned with the standard speed for that aircraft configuration and that stage of the flight. The pilot then watched the speed discrepancy reduce until the right PFD indicated the same speed as the left PFD. At this point, the pilot suspected that the covers had been left on the pitot tubes as they did not recall removing them before departure, and that the covers had now fallen off and speed indications had returned to normal.
The pilot therefore began comparing various data sources to verify the aircraft’s climb speed and performance. The pilot cross-checked the aircraft’s groundspeed[5] and true airspeed (KTAS)[6] on the multi‑function display (MFD), as well as with the aircraft’s air data computer and GPS indications. The pilot also compared the indicated altitude with the GPS altitude from OzRunways. As the aircraft parameters were consistent with normal flight conditions, the pilot elected to continue with the flight and landed without incident at Numbulwar.
After landing in Numbulwar, the pilot conducted a detailed visual inspection of both the pitot tubes and the aircraft in general. During this inspection, they found the remnants of the pitot covers still fitted to the tubes. As the pitot heat system had been turned on during flight, the covers on both tubes had partially melted, however the pilot noted no damage or debris in the actual pitot tubes. The aircraft had flown around 40 minutes and 250 km over remote, unlit terrain in this configuration. After conducting this inspection, the pilot determined it was safe to conduct the next sector to Darwin.
Similarities to previous incidents
The pitot tube issue on 23 July 2024 was not the first such incident involving this operator on this aircraft type. In May 2024, the ATSB reported on an occurrence where an aircraft departed from Darwin Airport with the pitot covers blocking the pitot tubes.[7] On that occasion, the pilot attempted to remove the pitot covers before departure but did not realise that the right-side streamer had detached from the right-side cover.
The pilot thought that the pitot covers had been removed entirely, and proceeded to take-off with the right pitot tube cover still in place. The pilot noticed an airspeed mismatch during rotation, and subsequently climbed to circuit height and returned to land. In both the May 2024 and July 2024 incidents, an airspeed discrepancy or mismatch did not become apparent until it was too late to reject the take-off.
Safety action
In response to this incident, the operator launched an internal investigation and undertook a series of safety actions to address the risks associated with blocked pitot tubes.
To reduce the risk of pitot covers being missed during the pre-flight inspection, the operator has purchased high visibility pitot tube cover flags, with the wording ‘remove before flight’, to be used on all fixed-wing aircraft in the operator’s fleet. Processes are also being established around the ongoing inspection and maintenance of these flags to ensure they are free from contamination and that their visibility is not compromised in low-light situations.
To mitigate the risk of errant speed indications, the operator is also sourcing leather covers for the B200 fleet that do not have a small vent hole. This addressed the potential for the small vent hole in the existing covers to allow sufficient airflow into the pitot system to provide a symmetric, albeit incorrect, speed indication during the take‑off roll. The new leather covers would prevent the generation of any airspeed indications at all, which would indicate blocked pitot tubes significantly earlier in the take‑off run and increase the likelihood of a safe rejected take‑off.
To assist pilots with managing inflight pitot tube issues, the operator is looking to introduce training on partially-blocked pitot tubes. This training will include a startle/surprise element to ensure pilots can respond appropriately to pitot blockages and errant speed indications. This is intended to be a key safety focus item in their simulator-based recurrent training and proficiency checks, and will cover all flight crew within the next six months.
Safety message
This incident highlights the importance of conducting an airspeed check early in the take‑off run. This allows the take-off to be rejected as soon as a mismatch is detected. In circumstances where a rejected take-off is not possible, pilots should follow the standard climb-out procedure then seek to land as soon as practicable. Although the B200 stall warning system operates independently of the pitot system, unreliable speed indications can increase the risk of aerodynamic stall[8] and subsequent loss of control, and several accidents internationally have been attributed to blocked pitot tubes.
This incident also illustrates the importance of maintaining a high level of attention and awareness when doing visual inspections of critical aircraft systems pre-flight, particularly at night. It is vital that the pitot tubes and static ports are fully uncovered and free from obvious obstructions, contamination, or damage prior to departure. Pilots should also remain cognisant of the risk that pitot covers may not be sufficiently conspicuous when installed on the aircraft, and follow standard procedures when fitting or removing these items. Targeted inspections of specific aircraft components, along with secondary means of accounting for ground-based protective equipment, can provide an extra layer of assurance that these items have been removed from the aircraft and are safely stowed prior to departure.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
[1] Pitot tubes are part of the aircraft's pitot-static system and are used to compute the aircraft's indicated airspeed.
[2] Aircraft wheel chocks are safety devices that prevent an aircraft from moving while it is parked. They are usually solid blocks of sturdy material and placed in front of and behind the wheels after the aircraft is parked.
[3] KIAS: indicated airspeed expressed in knots, used by pilots as a reference for all aircraft manoeuvres.
[4] Rotation: the positive, nose-up, movement of an aircraft about the lateral (pitch) axis immediately before becoming airborne.
[5] Groundspeed: an aircraft’s horizontal speed relative to the ground.
[6] KTAS: true airspeed expressed in knots, used by pilots for pre-departure flight planning and navigation purposes.
[7] Flight preparation event involving Hawker Beechcraft Corporation B200, Darwin Airport, Northern Territory, on 8 May 2024 (AB-2024-025).
[8] Aerodynamic stall: occurs when airflow separates from the wing’s upper surface and becomes turbulent. A stall occurs at high angles of attack, typically 16˚ to 18˚, and results in reduced lift.