- COLLISION AVOIDANCE
The Seven-Point Scan
To properly scan, seven points must be used, the first is in the “7-thirty” position behind the students left shoulder, the second is the “9-o’clock” position off the left wing, the next is the “10-thirty” position between the aircraft nose and left wing, then the “12-o’clock” position off the nose, the “1-thirty” position between the nose and right wing, the “3-o’clock” position off the right wing, and the “4-thirty” position behind the Instructor’s right shoulder.
Some important considerations with regard to technique: to properly scan, you should for each of the scan points described above first select a distant eye-focus point—e.g., a distant cloud or mountain—and focus momentarily on this point, keeping your eyes still—if another aircraft is out there, you will detect its movement. For the same point, now focus on a nearer point—say a four-finger distance below the horizon. Again, focus on this point keeping your eye still to allow the detection of movement. This technique is used for all seven points.
While a proper scan utilizes the movement of targets for the detection of air traffic, there is an ironic contradiction that you must be aware of—if an approaching aircraft appears fixed in the windscreen, you are on a collision course. In contrast, if the approaching aircraft has movement, there is no risk of collision. So while your scanning should centre on moving targets, be aware that it is the fixed targets that can kill. With fixed targets, the 12-o’clock position is the most dangerous—owing, primarily, to the short time to impact. While fixed targets can approach from virtually any direction, positions other than the 12-o’clock provide relatively longer time for detection and evasive action.
Areas of Risk
A small percentage of mid-air collisions occur head on; nearly all occur in daylight hours in VFR conditions within 5 nautical miles of an airport, usually in the traffic circuit. Additionally, a pilot is five-times more likely to have a mid-air with an aircraft flying in the same direction than with one flying in the opposite direction. Never turn, climb, or descend into a blind spot. During flight, the critical areas to scan are 60° left and right of the flight path, and 10° above and below. In this area the relative airspeed of both aircraft, even if small aircraft, can easily be 250 KNOTS or 455 km/hr—a speed that is hard to conceive of and which provides little time for collision avoidance. Before and during a prolonged descent, turn to clear the airspace below you.
Clearing Airspace Prior to Turns
A high level of risk for collision exists during a turn. For this reason, it is required that all Langley Flying School students call “clear left” or “clear right” prior to initiating a turn. This rule applies to all flight training. Your instructor will likely stop the turn if this call is not made.
Risks during Climbs and Descents
There is no reason for an aircraft to fly straight and level. There is no cost to making turns, and if turns are performed properly—with smoothness and gentleness— the passengers won’t even be aware that a turn is occurring. If the aircraft is flying straight and level, its movement is predictable to vicinity aircraft, the pilot of which can take whatever action is required to keep clear. The circumstances are very different when an aircraft begins to climb or descend—the actions of the aircraft cannot be predicted by others, and this is especially the case if the climbs or descents are made aggressively or rapidly. For this reason, prior to beginning a climb or descent, it is crucial to perform gentle clearing turns left and right—just enough to ensure there is no other traffic directly above or below the aircraft. There is no cost to this manoeuvre, it only takes a second, and it could save your life and the lives of your passengers. For students at Langley Flying School, it is mandatory to call “clear left and right” prior to initiating a climb or descent.
Clearing Turns during Climbs
You are especially vulnerable to mid-air collisions during a climb, the reason being that forward visibility is obscured by the engine cowling. For this reason, once the aircraft departs from the circuit (climbs through 1000’ AGL), you should begin a series of gentle turns, left and right, so that the blind spot is cleared. To do this, use 15° of bank, and turn to a heading approximately 30° (to turn further serves no purpose, and turning to a lesser heading will not clear the entire blind spot. To keep on track, the second clearing turn should be done in the opposite direction. During a climb, a clearing turn should be performed approximately every 30 seconds. While you are encouraged to turn frequently during a climb, do so smoothly and gently.
For the first 1000’ of the departure from a runway, a clearing turn cannot be performed (unless you feel traffic circumstances warrant it), so before you apply power for takeoff, scan the departure end of the runway for potential traffic hazards—if you see one during the initial climb, manoeuvre to protect your safety.
Transport Canada's flight operation
U.S. Federal Aviation Administration's How to Avoid a Mid-air Collison
Austrailian Transport Safety Bureau's Limitations of See-and-Avoid Principle
AOPA's Collision Avoidance: Strategies and Tactics
Collision Avoidance Systems, Wikipedia