Yukiko kakimoto, Ph.D
It has been nearly 100 years since the Wright Brothers flew for the first time in the history of aviation. During these 100 years, the technology of aircraft structure and cockpit function have developed significantly. And moreover, aircraft numbers are increasing worldwide. The accidents rate par million departure has decreased significantly comparing with the first stage of commercial airlines, but the accident rate 1.0 par 100 million departure has not been changing since these 20 years , it is 10-6 level. Actual numbers of accidents occur nearly 20 - 30 cases every year worldwide and nearly 300 people are fatalities. Among these aircraft accidents, inadequate communication between pilots and air traffic controllers attributed to direct causes of aviation accident frequently.
The reason why inadequate communication errors occur between pilots and ATC (Air traffic controller) might be considered that they have to communicate through radio communication and they can not know operating or controlling situations each others. They can not have the interfaces to know situations on both side. In the current systems of aviation , every aircraft can not take off and land without the clearance from ATC through radio communication.
Radio communication sometimes cause misunderstanding, loss of communication, or wrong instruction against their intention, etc. on both ATC side and pilots side. In most of cases, pilots hesitated to ask again to confirm the content of communication because of congestion of communication or their pride to ask again. On the other hand, ATC controllers do not confirm only occasionally the content of Readback/ Hearback under busy traffic.
In this report, recent incidents/troubles concerning to communication problems between ATC and pilots will be analyzed and discussed.
The role of ATC will be briefly described here. Roughly, their work is divided into two areas ; that is, Terminal ATC and En-route ACC( Area Control Center ). Terminal ATC are in every airport, and there are four ACCs are in our country ; Sapporo ACC, Tokyo ACC, Fukuoka ACC, and NAHA ACC.
Terminal Air Traffic Controllers control usually the area of a cone( distance; radius 9km, height; 24,000ft, and there are some exceptions.). Finally Terminal controllers hand off their controlling aircraft to en-route( ACC ) controllers . Moreover, terminal ATC is divided into Tower and Radar works.
In the Tower, there are three roles independently ; grand control, coordinate control, and local control. Among three roles, a local controller has a responsibility to give pilots Take off and Landing clearance and this position is always busy where usually they control simultaneously 10-14 aircraft. Each three role is independently and each controller performs their information processing independently. The more traffic numbers are increasing, the more controllers’ workload is increasing. As a custom, they change their position every one hour within their crew to maintain required attention level.
Each controller works indepently by each position. Their works are depending on significantly much their memory. As their reminder, they use a strip card par each aircraft which has long history. ATC controllers erase the items finished using their hand on a strip card. When all items are completed, that strip card are thrown away. It is considered that to use their hand might strengthen their reminds, but not enough.
Within these a few years , they have begun to use displays through personal computers as their reminder interfaces. For example, the information on closed Runway or current weather is indicated on their displays on time.
Case 1 (Jan.31, 2001 around 15:55): Near midair collision between A/c A (JAL 907) and A/c B (JAL 958) occurred over the sea off Yaizu city, Shizuoka prefecture, Japan. 100 people injured ( 2 cabin attendants and 7 passengers seriously injured ) by acute descent and climb to avoid collision (Figure).
A controller trainee issued the instruction to A/c A to descend against his intention to issue the instruction to A/c B. This is an error issued different call sign against his intention.
The controller trainee and his supervisor noticed unusual clearance between two aircraft through CNF (Conflict Alert ) by blinking red lamp on the radar.
On the other hands, two aircraft each has TCAS (Traffic Alert and Collision Avoidance System) . It is a kind of interfaces to let them know possibility of midair collision. However, A/c A followed the controller’s instruction “ Descend and maintain to 35,000ft” against instruction by TCAS RA “Climb, Climb” and on the other hands, A/c B followed the instruction of TCAS RA “ Descend, Descend” and continued descending.
TCAS is designed to detect an aircraft that is a collision risk and issues Traffic Advisory ( TA ) alerts to advise their positions and Resolution Advisory (RA) commands to avoid collision.
The TCAS installed in an aircraft interrogates the transponders of all nearby aircraft and obtains their distance and altitude from the replies received. Based on relative speed and rate of change of altitude information computed by the TCAS logic from the distance and altitude, the TCAS calculates the time to the Closest Point of Approach ( CPA) with the other aircraft and determines whether or not there is a threat of collision. When TCAS judges another aircraft to be a collision threat, if the other aircraft is also TCAS-equipped the TCAS sends it a coordination signal to resolve the encounter; for example, when TCAS selects an upward sense RA ( to instruct the pilot to climb ), it will transmit a coordination signal to the TCAS on the other aircraft to restrict its RA selection to the downward sense( to instruct to the other aircraft’s pilot to descend). The TCAS also issue a synthetic voice warning together with an indication on the TCAS display devise the pilot how to maneuver to avoid the encounter.( concerning to explanation of TCAS, the author adopted from 2002-5, Aircraft Accident Investigation report by Aviation and Railways Accident Investigation Commission).
TCAS is highly computerized system to avoid midair collision. Every commercial aircraft has these system , but it depends on pilots how to use these. Moreover, it is not clear that if there are contradiction between TCAS RA and a controller’s advice, how pilots perform. On the other hands, CNF on radar in Tokyo ACC is also a reminder for controllers. It began to blink just 56 sec before to attain nearest distance between A/c A and A/c B. Usually the CNF blinks 3 minutes before two aircraft are approaching, but in this case, it blinked 56sec before because A/c A was turning and climbing to left . CNF can not adequately respond to changes of aircraft attitude. This means CNF is not sufficient for a reminder.
This near midair collision revealed the problem how do we do when the TCAS instruction is different from the instruction from Air Traffic Controllers. This case might be the first case worldwide involving the contradiction between TCAS RA instruction and a controller’s instruction.
ICAO recommended all over the world to follow TCAS advice when there exists contradiction between ATC instruction and that of the TCAS RA based on a recommendation from the Commission of Aircraft and Railways Accident Investigation, Japan.
Case 2 ( April 29, 2003) : The Incident occurred on the Runway A in Tokyo International Airport, Haneda
The local controller cleared to A/c A to land to R/w A. The captain of A/c A had the information at Take off Airport of Chitose that R/w A is closed for traffic because of construction works . So when the captain got the clearance from the controller, he asked to the controller “ Confirm Runway three –four left ,Okay? ” The controller responded immediately “ Runway three-four –Lima, cleared to land.” Then A/c A actually landed on Runway 34L. Fortunately nothing occurred because the construction had not yet begun. The information of Runway closed never reminded through displays in Tower. The controller who was taking charge of informing to all crew members did not inform them by his misjudging of preconceived idea the construction had not yet started. The local controller focused on other aircraft under busy time and never checked the information of R/w A close.
The computer itself has a characteristics to give information as a reminder, but controllers cannot use these adequately because local controllers have to watch carefully approaching aircraft with head up posture and standing on specially busy time. So they are difficult to see the display by head down posture. To use reminders effectively, it is requested to install head up displays.
Case 3 (March 20, 2009) : This case is an incident occurred in Itami Airport, Osaka
ANA 18 aircraft expected to receive take off clearance next, then they heard from the local controller “ ANA 181 aircraft cleared for take off “. So they realized this instruction issued for them. ANA 18 could not know the similar call sign 181 existed at the same time. So ANA 18 entered into Runway B. An approaching another aircraft JEX 2200 noticed the Aircraft in the Runway B and JEX 2200 did go around. The local controller noticed runway incursion by the report of go around by JEX 2200. From the controller seat, Runway B is far and the controller did not notice the ANA 18 entered into Runway B. After that the controller performed completely. For local controllers, they had not the idea that similar call sign existed under daily works.
In this incident, it is realized that the similar call sign involves serious problems. From view point of interfaces, pilots do not have the system to know other aircrafts information and the other aircraft movement on the ground in the airport.
The following table shows the problems of these cases using SHEL model (Hawkins,F.H.1975 )
Table Interfaces Problems by SHEL model
CNF blinked 56sec. for turning aircraft ATC cannot receive TCAS information on radar( this time it was improved)
A Local controller could not utilize the information on the display in Tower as a reminder.
Pilots could not notisfy the existence of other aircraft information. They do not have such a remainder
There was not clearly procedure when a pilot receive the instruction which involved contradiction between TCAS RA and a controller.
Preconceived idea disturbed adequate use of an indicater as a reminder.
It is requested to improve the existence of similar call sign at the same time and at the same place
Air Traffic Controllers and Pilots
How to perform adequate Communication between Air Traffic Controller and pilots.
ATC works are independent and required concentrative attention.
ATC is depending upon memory.
Controller and Environment
The Airport of case 2 is not useful structure for ATC controllers.
Communication between Pilots and Air traffic Controllers is performed through radio communication. Only occationally one word from a controller caused serious tragedy in the history of aviation accidents/incidents.
The work of Air Traffic Controllers can not divide like a cockpit crew. So it is said that the work of ATC is very high workload within limited time.
Afterward, the improvement of interfaces is requested more under the environment of current Airport and traffic numbers are increasing worldwide.
 Connell,L: Pilot and Controller Communication Issues
 Yukiko Kakimoto: Transport Accidents and Human Errors, edited by Oyama,T & Maruyama,Y “ Science of Human Errors”, 2004, Reitaku Univ.(in Japanese)
 Aviation & Railways Accident Investigation Commission: Aviation Accident Investigation Report, 2002( in English)
 Aviation & Railways Accident Investigation Commission: Aviation Accident Investigation Report, 2005( in Japanese)
Dr. Yukiko Kakimoto worked at Aeromedical Laboratory, JASDF, Tokyo for nearly 30 years as a research psychologist. She studied fatigue management for pilot and ATC, how to evaluate pilots and air traffic controllers workload, human errors analysis caused by aviation accident/incidents in JASDF. She moved to Jissen Women’s University as a full time professor in Apr. 2000 and there she taught human factors, ergonomics and experimental psychology. Simultaneously during the period from 2001-2007, she was working as a member of Aircraft and Railways Accident Investigation Commission of Japanese Government. After retirement in 2007, she has worked at Japan Institute of Human Factors and as a part time professor of Rissho University. She is the Technical Program chair of the Congress of ISASI (International Society of Aviation Safety Investigators) to be held in Sapporo Japan in September 2010.