Every pilot's worst nightmare is the thought of a collision with another aircraft. History shows that it can be just as catastrophic on the ground as in the air.
The industry's worst disaster remains the collision between two Boeing 747s on the runway at Tenerife in 1977, in which 583 people died.
According to the Federal Aviation Administration, the number one aviation safety issue in the United States is now runway incursions, which are occurring at a rate of about 230 a year.
In Australia the figures are a lot lower. The ATSB recorded a total of 89 runway incursions in 1996, 130 in 1998, and 113 in 1999.
Unlike the US, Australia has considerably fewer airports in controlled airspace and less daily traffic movement. But the numbers are significant enough to warrant closer inspection for trends and safety implications.
A runway incursion is an occurrence at an airport with an operating air traffic control tower that involves an aircraft, vehicle, person, animals or another object on the ground, and which creates a collision hazard or results in a loss of air traffic separation.
Using the Systemic Incident Analysis Model, [SIAM was described on page 33 in the last issue of Flight Safety Australia], an analysis of occurrence reports held by the ATSB reveals that the majority of runway incursions involve a failure to follow air traffic control instructions.
Approximately 85 per cent of runway incursions in the period 1997-1999 occurred after the failure of the defence of 'ATS procedures, facilities and standards'. Of the ATS failures, nearly 94 per cent are further classified as 'clearances and instructions' failures. In just over 90 per cent of the incursions, Air Traffic Services noticed the problem, and the situation did not become more serious.
The following example shows how a series of events can lead to a runway incursion, starting with a failure to follow instructions.
On Wednesday 22 July 1998 at Sydney airport a Boeing 737 and a Metro 111 narrowly avoided collision at the intersection of taxiway Juliet and runway 34L.
The Metro pilot was taxiing the aircraft on taxiway Juliet with instructions to taxi via taxiway Bravo and hold short of runway 25. The pilot read back the instructions correctly.
The pilot had experienced difficulties during a practice ILS approach under the supervision of a training captain and was distracted with thoughts of his performance. The training captain left it too late to warn the pilot that he had taxied the aircraft past the correct taxiway turn-off and only called for him to stop when he saw the aircraft landing on runway 34L.
The 737 was landing on runway 34L at the same time that the Metro overshot the runway holding point. The pilot could not stop the aircraft before the taxiway entry point and passed to the left of the runway centre line to keep clear of the Metro. It cleared it by about 25 metres while travelling at 80 knots.
The air traffic controller called for the Metro to stop about the same time as the check captain. The prompt action of the tower controllers was the final safety defence which stopped the aircraft from entering the runway.
Other examples show how incomplete communication and air traffic control actions can lead to a runway incursion.
On 14 May 1999 a Navajo Chieftain lined up on runway 34L at the intersection of taxiway B10 at Sydney at night. A Saab 340 had been cleared to depart prior to the Chieftain. Another Saab 340 was on final approach to land on the same runway.
When the departing Saab had been cleared to take off the arriving Saab was cleared to land. The pilot of the Chieftain was then given a conditional clearance to line-up on the runway behind the landing aircraft. In the same transmission, the pilot was also given instruction regarding the direction of turn and heading to adopt after becoming airborne.
The pilot of the Chieftain heard the line-up clearance and after take off instructions, but did not hear the condition that the aircraft should line up behind the landing aircraft. The pilot read back the instructions that he heard, but the controller did not notice that the condition on the line-up clearance was not read back.
The Chieftain lined up on the runway, sighted the aircraft on final approach to runway 34L, and expected an immediate take off clearance. The crew of the Saab noticed an aircraft on the runway and after contacting the tower commenced a go-round from a height of approximately 35 feet, overflying the Chieftain at a height of about 150 feet.
The controller had correctly issued the take off instruction, but did not detect the incomplete read back by the pilot. The controller did not notice with a normal visual scan or by referring to the surface movement radar that the Chieftain had already entered the runway contrary to its assigned clearance.
While system defences work by preventing a serious accident on many occasions, occurrence reports will often highlight the potential for a breach in the defences, leading to safety action to rectify a deficiency before it contributed to an accident.
At Perth airport on 9 October 1997 a B767 landed on runway 21 while a B737 was on final for runway 24. Visibility from the tower was poor due to low cloud and fog.
The controller reported that he was unable to see either runway clearly. As the B767 turned off runway 21 onto taxiway J the crew were instructed to hold short of runway 24. They were unable to comply with this instruction as their aircraft was already two to three metres past the holding point for runway 24. They reported their position to the controller who then instructed the crew of the B737 to go round. The B737 was 3 nm from the runway at the time.
The pilot in command of the B767 reported that he had not previously used taxiway J and that in the limited visibility the aircraft had reached runway 24 more quickly than expected. Although they had attempted to stop short of runway 24 the aircraft passed the holding point before all movement ceased.
Had the crew of the B767 not reported its situation immediately there were no other defences to prevent a possible collision between the aircraft.
Key safety messages
While the figures in the Bureau's database represent only those occurrences in an active control zone they also highlight safety issues that apply to operations at non-controlled aerodromes.
The importance of pilot look-out, clear radio communications and go-round procedures feature regularly as one of the key safety messages, as the following catastrophic accident in the United States shows.
At Quincy Municipal Airport in November 1996 a number of passengers and crew were fatally injured when two aircraft collided at the intersection of two runways.
A Beech 1900C made a straight-in approach in visual conditions to Runway 13. At the same time, a Beech King Air began its take-off roll on Runway 04. Waiting behind the King Air was a Piper Cherokee (PA28).
The captain of the Beech 1900C reported his aircraft was on short final for Runway 13. He asked whether the aircraft in position on Runway 04 was holding or about to take off.
The King Air pilot did not respond, but the pilot of the PA28 did, and stated it was holding for departure on runway four. The US National Transportation Safety Board's (NTSB) report found the PA28 pilot's response to the Beech pilot's question was inappropriate since the PA28 was behind the King Air and not first in line for take-off.
Despite evasive action by the pilots of both aircraft, the Beech and the King Air collided on the ground at the intersection of the two runways. The weather was not a factor and all the pilots involved were properly rated, trained and qualified.
The NTSB determined the probable cause of the accident to be the failure of the King Air crew to effectively monitor the common traffic advisory frequency (CTAF.) Also implicated was their failure to scan for traffic. Contributing to the cause of the accident was the PA28 pilot's interruptive radio transmission. The crew of the Beech misunderstood his message.
In its discussion of the human factors involved in the accident, the NTSB concluded that the radio transmission by the PA28 pilot created some of the confusion that precipitated the accident. The pilot of the King Air was a retired airline captain and known to usually be in a hurry to get home. It is possible the crew in the King Air were not monitoring the CTAF.
Industry safety success
The key to the aviation industry's success in developing into a safe system is its defences. Many elements such as procedures, and hardware and software, play a part in providing a defence against the consequences of human error. When one or more of these system defences are breached, an incident can happen. If they fail, an accident may be the outcome.
The best defences against the hazards of runway incursions are by compliance with procedures, and for pilots to cross check and monitor their environment and actions to maintain situational awareness.
Put yourself in the position of the pilot in the occurrences described above. What would you have done? More importantly, what will you do from now on?*
|Type:||Educational Fact Sheet|
|Publication date:||11 April 2001|