Take-off without ATC Clearance
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|Category:||Air Ground Communication|
Take-off without ATC Clearance is an aerodrome-related safety event that is somewhat similar to Landing without ATC Clearance. Both involve air traffic control, typically happen during critical and high-workload stages of the flight, and can result in similar hazardous outcomes (e.g. runway incursion, loss of separation, collision, etc.).
The main difference between the two events (aside from the flight phase) are the causal factors involved. Landing without ATC clearance can be caused by one or more of a variety of factors - loss of communication, loss of situational awareness (e.g. unintentional use of an incorrect runway, taxiway or even aerodrome), poor communication, high workload, etc. In the takeoff without ATC clearance scenario, poor pilot-controller communication (e.g. improper phraseology) is by far the most common precursor. Normally, if a flight crew finds out that there is a communication failure during the taxi phase, they will return to apron to investigate and will not attempt to take off. Also, while the inadvertent use of a wrong runway (or a taxiway) for take off sometimes happens, it is impossible to imagine that a pilot would try to use a wrong aerodrome.
Note: this article does not examine scenarios in which a valid takeoff clearance is given but is not followed correctly due to the aircraft being in the wrong place (i.e., attempting takeoff from a taxiway or from a wrong runway).
Taking off without ATC clearance may lead to:
- Runway Incursion - The aircraft may have been cleared only to the runway holding point. Also, at relatively complex aerodromes, taking off may mean crossing other runways.
- Rejected Take Off - The tower controller would likely observe the aircraft starting the take-off roll and may instruct the crew to cancel it.
- Loss of Separation - If the take-off without clearance is not aborted, either because of lack of communication or due to the pilots non-compliance with the instruction (e.g. for safety reasons), there is a chance that the aircraft that has just taken off will come into close proximity with other traffic in the vicinity of the aerodrome.
- Aborted landing(s) for aircraft on final. This may happen as a consequence of a runway incursion.
- Increased workloads for controllers and pilots due to the sudden change of plan. At busier aerodromes, several aircraft may need to be given avoiding-action instructions or other clearance amendments (e.g. orbits/holding patterns).
- Call sign confusion (i.e., the flight crew of one aircraft taking a clearance intended for another one) - This is more likely to happen at complex aerodromes with more than one runway.
- Incorrect phraseology - The most notorious example of this is the use of the word take-off in a phrase not related to a take-off clearance but instead to a different type of ATC clearance; see (the B742 / B741, Tenerife Canary Islands Spain, 1977 accident). A distorted ATC message containing the word "take off" can easily be misinterpreted as a takeoff clearance.
- Expectation bias - For example, the instruction "for departure contact tower" issued by the GND controller might be misinterpreted as "after departure contact tower." This was the case in the B738, Eindhoven Netherlands, 2012 occurrence.
- Cockpit workload - The pre-takeoff part of the flight is a time of high workload for pilots, and there is risk that they will fail to notice the absence of a clearance or "will assume" that their take-off clearance has been issued.
- Strict adherence to SOPs - If in doubt whether a take-off clearance has been received, the flight crew should clarify the situation with the tower controller.
- Radiotelephony discipline - While standard phraseology and proper communication techniques should be followed at all times, the following aspects must be stressed in relation to the risk of takeoff without ATC clearance:
- The phrase take off should only be used by ATC when issuing or cancelling a take-off clearance. In all other instances departure or airborne should be used.
- A blocked frequency often means that two aircraft (usually with similar call signs) have accepted the same clearance. The controller should promptly intervene in such circumstances to clarify the situation. Pilots, if in doubt whether a clearance was meant for them, should clarify rather than assume.
- Incorrect readback detection. An incorrect readback may mean that the pilot has confirmed what he or she thought they heard or expected to hear (e.g., line up, cleared for take-off) and not the actual clearance (e.g., line up and wait).
- Unambiguous hold short, line up and take off clearances - If the controller has any doubt that the crew might interpret the clearance incorrectly, they should emphasise (restate) the relevant part of the clearance. If the flight crew has any doubt about whether or not the clearance received contains a take-off part they should seek clarification instead of assuming "the most probable" scenario.
- Proper handling of conditional clearances - Normally, conditional clearances should be used by ATC for line up clearance, and not for take-off clearance. Controllers should explicitly state that a further (take-off) clearance is to be issued at a later time.
- Controller vigilance - If the controller observes that an aircraft has just started its take-off roll and there is any safety concern, the controller should instruct the flight crew to stop immediately. If the error is detected early enough, the rejected take off will have no negative impact on flight safety (operational efficiency may suffer, however, as the aircraft may need to lose time to taxi back to the beginning of the runway).
Accidents and Incidents
- AS32 / B734, Aberdeen UK, 2000 (For reasons that were not established, a Super Puma helicopter being air tested and in the hover at about 30 feet agl near the active runway at Aberdeen assumed that the departure clearance given by GND was a take off clearance and moved into the hover over the opposite end of the runway at the same time as a Boeing 737 was taking off. The 737 saw the helicopter ahead and made a high speed rejected take off, stopping approximately 100 metres before reaching the position of the helicopter which had by then moved off the runway still hovering.)
- B190 / B190, Auckland NZ, 2007 (On 1 August 2007, the crew of a Beech 1900 aircraft holding on an angled taxiway at Auckland International Airport mistakenly accepted the take-off clearance for another Beech 1900 that was waiting on the runway and which had a somewhat similar call sign. The pilots of both aircraft read back the clearance. The aerodrome controller heard, but did not react to, the crossed transmissions. The holding aircraft entered the runway in front of the cleared aircraft, which had commenced its take-off. The pilots of both aircraft took avoiding action and stopped on the runway without any damage or injury.)
- B463 / PA38 Birmingham UK, 1999 (On 28 April 1999, a BAe 146-300 departing Birmingham began its daylight take off from Runway 33 without ATC clearance just prior to the touchdown of a PA38 on the intersecting runway 06. Collision was very narrowly avoided after the Controller intervened and the BAe 146 rejected its take off, just missing the PA38 which had stopped just off the runway 33 centreline. The Investigation noted the 146 pilots belief that a take off clearance had been issued but also that no attempt appeared to have been made to read it back or confirm it with the First Officer.)
- B738, Eindhoven Netherlands, 2012 (On 11 October 2012, the crew of a Ryanair Boeing 737-800 did not change frequency to TWR when instructed to do so by GND whilst already backtracking the departure runway and then made a 180° turn and took off without clearance still on GND frequency. Whilst no actual loss of ground or airborne safety resulted, the Investigation found that when the Captain had queried the receipt of a take off clearance with the First Officer, he had received and accepted a hesitant confirmation. Crew non-compliance with related AIP ground manoeuvring restrictions replicated in their airport briefing was also noted.)
- B742 / B741, Tenerife Canary Islands Spain, 1977 (On 27 March 1977, a KLM Boeing 747-200 began its low visibility take-off at Tenerife without requesting or receiving take-off clearance and a collision with a Boeing 747-100 backtracking the same runway subsequently occurred. Both aircraft were destroyed by the impact and consequential fire and 583 people died. The Investigation attributed the crash primarily to the actions and inactions of the KLM Captain, who was the Operator's Chief Flying Instructor. Safety Recommendations made emphasised the importance of standard phraseology in all normal radio communications and avoidance of the phrase "take-off" in ATC Departure Clearances.)
- B744 / MD90, New Chitose Japan, 2008 (On 16 February 2008, during daylight and in poor visibility, a Boeing 747-400, operated by Japan Airlines, was holding on a taxiway next to runway 01R of New Chitose Airport, Japan. A Douglas MD-90-30 operated by the same airline landed on the same runway and was still on the runway when the B747 was cleared to line up and wait. Shortly after lineup the B747 began its takeoff roll without receiving such clearance and subsequently was instructed to abort the takeoff. The crew of the B747 successfully rejected the takeoff.)
- DH8B, Kangerlussuaq Greenland, 2017 (On 2 March 2017, a DHC8-200 took off from Kangerlussuaq in normal day visibility without clearance and almost immediately overflew three snow clearance vehicles on the runway. The Investigation identified a number of likely contributory factors including a one hour departure delay which the crew were keen to reduce in order to remain within their maximum allowable duty period and their inability to initially see the vehicles because of the runway down slope. No evidence of crew fatigue was found; it was noted that the vehicles involved had been in contact with TWR on a separate frequency using the local language.)
- E195 / A320, Brussels Belgium, 2016 (On 5 October 2016, an Embraer 195 took off at night without clearance as an Airbus A320 was about to touch down on an intersecting runway. The A320 responded promptly to the ATC go-around instruction and passed over the intersection after the E195 had accelerated through it during its take-off roll. The Investigation found that the E195 crew had correctly acknowledged a 'line up and wait' instruction but then commenced their take-off without stopping. Inadequate crew cross-checking procedures at the E195 operator and ATC use of intermediate runway access for intersecting runway take-offs were identified as contributory factors.)