This article describes good practices that could be used by air traffic controllers to prevent landing without clearance occurrences. It provides reference to the existing ATC prevention barriers, best practices and lessons learned.
Automated Tools and Systems
Automated tools and systems do not require controller’s input to operate. Most of these systems (FAROS, RWSL, RAAS, EVS) are targeted at the flight crew and provide additional layers of protection against hazardous landings. Surveillance systems (e.g. A-SMGCS), on the other hand provide the controller with means to enhance their situational awareness, especially:
- In poor visibility conditions;
- If parts of the manoeuvring area are not visible from the tower due to obstructions;
- When an unknown aircraft that has not checked in on the frequency approaches the runway threshold (e.g. entering the CTR from uncontrolled airspace).
Also, surveillance systems can be very helpful in mitigating human error, e.g.:
- Aircraft not communicating with the tower due to various reasons, e.g.:
- Crew transferred from approach to tower too early;
- Crew tuning a wrong frequency;
- Crew tuning the correct frequency but not checking in.
- Aircraft approaching the wrong runway due to loss of positional orientation;
- The controller forgetting about an aircraft on final.
Controller Memory Aids
Controllers memory aids are used to assist the controller in maintaining situational awareness. These require manual input. The most common memory aids are:
- Flight strip positioning rules – placing flight strips in specific locations according to the clearances issued;
- Electronic or handwritten marks on the flight strips (e.g. a tick when a landing clearance is given);
- Switches – a simple on/off switch with a corresponding sign (e.g. “runway occupied”) might be useful for maintaining situational awareness and the controller remembering that a clearance has been given to the (approaching) aircraft.
Procedures and Best Practices
The advice in this section is derived from common sense, best practices and lessons learned from relevant studies. It is not intended to supersede or replace local instructions and procedures.
- Visual inspection before issuing a clearance for runway entery or crossing – this may reveal a (possibly unknown or forgotten) aircraft that is about to land without a clearance.
- Visual observation of all traffic to confirm all clearances are properly complied with. The probability that an aircraft (with a valid landing clearance) may attempt to land on a wrong runway or taxiway should always be considered.
- Maintenance of situational awareness is critical. Forgetting about an aircraft being on the final is a common reason for landing without clearance. Establishing and following procedures for strip handling (e.g. placing marks or moving the paper strips) can be a simple and effective solution;
- Coordination with adjacent units (especially approach units) is essential. If the situation permits, the tower should be advised that an aircraft is about to call. If this is not possible due to congested traffic a procedure for electronic handover/takeover may be considered.
- Relying only on pilot reports in congested traffic situations is sometimes not advisable. The pilots may forget that they need to make a position report or they may not be able to do it due to the high frequency occupancy. In some cases, assistance from the approach could be helpful if the situation permits (e.g. the approach controller advises the tower via hotline when an aircraft is over a specified position). Surveillance systems such as ASMGCS might also be a viable option;
- Strict adherence to standard phraseology and readback/hearback procedures is essential for preventing misunderstandings and detecting expectation bias. This is especially true for “expect landing clearance” instructions.
- The overall use of the phrase “expect landing clearance” might need to be considered. Generally, a pilot approaching an aerodrome is expecting a landing clearance anyway and will continue to expect it regardless of whether a specific instruction for this is received. It may be a good idea to use the phrase on special occasions only (e.g. if a training or an airworthiness flight is intending to perform a go-around or a touch-and-go).
Sometimes aircraft land without a clearance even though all ATC procedures are strictly followed and all memory aids are used correctly. The process has two independent sides (ATC and flight crew) and each of them may contribute to an event on their own. If the controller spots an aircraft that has (almost) touched down without having received a landing clearance, the following factors need to be considered:
- Instructing the flight crew to go around or even informing them that they have no valid landing clearance might worsen the situation. The crew (being startled by the fact) may execute and abrupt manoeuvre resulting ultimately in loss of control, tail strike, runway excursion.
- A go-around instruction might sometimes be a safer option if there is imminent collision danger (e.g. there is another aircraft or vehicle on the runway and it would not be able to vacate in time).