Communication errors between pilots and air traffic control
Aviation communication errors are critical to the safety of aircrafts. Minor errors have the potential to result in catastrophic situations. Studies of real transmissions (Cardosi, 1994; Lee and Rodvold, 1993) suggested that less than 1% of all radio transmissions contain errors.
The reasons for these errors are:
|Radio Transmission Errors||Percentage|
|No pilot readback||25%|
|Hearback errors type 2||18%|
A readback error is defined as an important discrepancy between the clearance which the controller issues, and what the pilot reads back. When the controller fails to correct the discrepancy, this becomes a hearback error. These errors are the most common type of communication error within the aviation industry, and there are multiple reasons for which they occur.
The following table shows the major reasons leading to these errors:
|Factors Perceived To Contribute To Readback/Hearback Errors||Percentage|
Possible ways to reduce the readback/hearback errors are to identify and notify pilots of similar callsigns, and have controllers speaking clearly and slowly, giving clear and concise clearances regardless of their workload (given that similar callsign and controller workload being the main causes). This would reduce the number of pilots making incorrect readbacks and requests to repeat clearances (which would reducing radio transmissions). Even though these errors are the most common, controllers pick up 66% on incorrect readbacks on average.
Of the incorrect hearback/readback errors from the sample, the following table shows the outcome of the errors:
|Results of Incorrect Readback/Hearback Errors||number|
|Less Than Standard Separation||35|
|Wrong Aircraft Accepted Clearance||30|
The two most common outcomes are altitude deviation and less than standard separation. All outcomes have the potential to create a chaotic situation and it is essential that pilots ensure they give a readback. Also, controllers must ensure a correct readback is received to minimise the chance of these errors occurring.
No Pilot Readback:
A lack of pilot readback ie ‘roger.’
Pilot expectation is the most common factor among the "No Pilot Readback." When a pilot expects to receive a specific clearance, and is given another, the pilot often assumes they have received the clearance they were expecting. If they responded with ‘roger’ or other response which does not readback the clearance, the controller is unaware that the pilot had misunderstood the clearance, and will expect them to do what they have been instructed. When the pilot does otherwise, there is potential for catastrophic situations to arise.
Altitude deviations and runway incursions are the only two significant implications of this error. Ways to reduce these errors are to ensure that readbacks given by the pilots and controllers are correct, regardless of workload. If correct readbacks are not received, flight strips should not be annotated by the controller as if they had been received, or they should be cocked to alert the controller the readback has not been received, and a readback needs to be attained be before any further action is taken. Pilots should also take responsibility to ensure they read back the required sections of the clearance to the controller.
Hearback Errors Type Two:
The controller fails to notice his or her own error in the pilots correct readback or fails to correct critical erroneous information in a pilots statement of intent. In many cases, the underlying reason for this error is unknown.
The following table shows the outcome of these errors:
|Results Associated With Hearback Errors Type Two||Number|
|Less Than Standard Separation||23|
|Controller Issued Clearance to Wrong Aircraft||7|
The most significant outcomes of these errors are less than standard separation and altitude deviation, both incredibly significant outcomes, in respect to safety. This, once again highlights the importance of readbacks and ensuring a correct readback is obtained. One simple way to improve the likelihood of achieving this is to limit the controllers' workload. Whether this means limiting the traffic, having more controllers working, or reducing sectors, it is important that the controllers are at their peak, and are not too busy so as to enable safe and efficient controlling. Pilots are also encouraged to question the controller should they be given an instruction or clearance that is not clear or seems wrong. This will make the controller check to ensure what they have issued is correct, and help pick up their errors. It is important that the pilots are not too intimidated to query the controller.
In summary, There are many factors contributing to the total communication problems within the aviation industry. Similar callsign is the biggest factor, closely followed by pilot expectation and controller workload.
This is shown in the table below:
|Factors Causing All Communication Errors||Number|
Many of the errors are either picked up by controllers, or result in little/ no implications in respect to the safety of the aircraft and separations imposed. However, other errors can result in massive implications. As mentioned, we have seen that errors can result in loss of standard separations, runway transgressions, altitude or heading/track deviations, clearances issued or readback by the wrong aircraft, as well as other errors. As any of these have the potential to create fatalaties, it is imperitive that both controllers and pilots are alert and focus their attention on their jobs. It is important for both controllers and pilots to speak slowly and clearly, regardless of their workload, and ensure correct readbacks are given or obtained. Controllers should also strive to ensure that clearances are clear and concise, and contain no more than four elements for pilots to read back. When similar callsigns are on the same frequencies, pilots should be notified of this, to increase their attention to the details, and minimise possibilities of error.
Clearly, many communication errors occur within the aviation industry. However, by working together and applying the above, errors and the potential for any serious incidents could be minimised. It is important for human factors to be taught to both pilots and controllers in their training so as to ensure an understanding of these factors and the implications that could be caused.
Federal Aviation Administration (Aug 1998). Pilot-Control Communication Errors: An Analysis of Aviation Safety Reporting System (ASRS) Report (DOT-VNTSC-FAA-98-4). Washington, DC: US Department of Transportation.