Title 14 of the CFR part 91 has established right-of-way rules, minimum safe altitudes, and VFR cruising altitudes to enhance flight safety. The pilot can contribute to collision avoidance by being alert and scanning for other aircraft. This is particularly important in the vicinity of an airport.

Effective scanning is accomplished with a series of short, regularly spaced eye movements that bring successive areas of the sky into the central visual field. Each movement should not exceed 10°, and each should be observed for at least 1 second to enable detection. Although back and forth eye movements seem preferred by most pilots, each pilot should develop a scanning pattern that is most comfortable and then adhere to it to assure optimum scanning. Even if entitled to the right-ofway, a pilot should yield if another aircraft seems too close.

Clearing Procedures

The following procedures and considerations are in place to assist pilots in collision avoidance under various situations:

  • Before takeoff – prior to taxiing onto a runway or landing area in preparation for takeoff, pilots should scan the approach area for possible landing traffic, executing appropriate maneuvers to provide a clear view of the approach areas.
  • Climbs and descents – during climbs and descents in flight conditions that permit visual detection of other traffic, pilots should execute gentle banks left and right at a frequency that permits continuous visual scanning of the airspace.
  • Straight and level – during sustained periods of straight-and-level flight, a pilot should execute appropriate clearing procedures at periodic intervals.
  • Traffic patterns – entries into traffic patterns while descending should be avoided.
  • Traffic at VOR sites – due to converging traffic, sustained vigilance should be maintained in the vicinity of VORs and intersections.
  • Training operations – vigilance should be maintained and clearing turns should be made prior to a practice maneuver. During instruction, the pilot should be asked to verbalize the clearing procedures (call out “clear left, right, above, and below”).
High-wing and low-wing aircraft have their respective blind spots. The pilot of a high-wing aircraft should momentarily raise the wing in the direction of the intended turn and look for traffic prior to commencing the turn. The pilot of a low-wing aircraft should momentarily lower the wing and look for traffic prior to commencing the turn.

Pilot Deviations (PDs)

A pilot deviation (PD) is an action of a pilot that violates any Federal Aviation Regulation. While PDs should be avoided, the regulations do authorize deviations from a clearance in response to a traffic alert and collision avoidance system resolution advisory. You must notify ATC as soon as possible following a deviation.Pilot deviations can occur in several different ways. Airborne deviations result when a pilot strays from an assigned heading or altitude or from an instrument procedure, or if the pilot penetrates controlled or restricted airspace without ATC clearance.

To prevent airborne deviations, follow these steps:

  • Plan each flight—you may have flown the flight many times before but conditions and situations can change rapidly, such as in the case of a pop-up temporary flight restriction (TFR). Take a few minutes prior to each flight to plan accordingly.
  • Talk and squawk—Proper communication with ATC has its benefits. Flight following often makes the controller’s job easier because they can better integrate VFR and IFR traffic.
  • Give yourself some room—GPS is usually more precise than ATC radar. Using your GPS to fly up to and along the line of the airspace you are trying to avoid could result in a pilot deviation because ATC radar may show you within the restricted airspace.

Ground deviations (also called surface deviations) include taxiing, taking off, or landing without clearance, deviating from an assigned taxi route, or failing to hold short of an assigned clearance limit. To prevent ground deviations, stay alert during ground operations. Pilot deviations can and frequently do occur on the ground. Many strategies and tactics pilots use to avoid airborne deviations also work on the ground.

Pilots should also remain vigilant about vehicle/pedestrian deviations (V/PDs). A vehicle or pedestrian deviation includes pedestrians, vehicles or other objects interfering with aircraft operations by entering or moving on the runway movement area without authorization from air traffic control. In serious instances, any ground deviation (PD or VPD) can result in a runway incursion. Best practices in preventing ground deviations can be found in the following section under runway incursion avoidance.

Runway Incursion Avoidance

A runway incursion is “any occurrence in the airport runway environment involving an aircraft, vehicle, person, or object on the ground that creates a collision hazard or results in a loss of required separation with an aircraft taking off, intending to take off, landing, or intending to land.” It is important to give the same attention to operating on the surface as in other phases of flights. Proper planning can prevent runway incursions and the possibility of a ground collision. A pilot should always be aware of the aircraft’s position on the surface at all times and be aware of other aircraft and vehicle operations on the airport. At times, towered airports can be busy and taxi instructions complex. In this situation, it may be advisable to write down taxi instructions. The following are some practices to help prevent a runway incursion:

  • Read back all runway crossing and/or hold instructions.
  • Review airport layouts as part of preflight planning, before descending to land and while taxiing, as needed.
  • Know airport signage.
  • Review NOTAM for information on runway/taxiway closures and construction areas.
  • Request progressive taxi instructions from ATC when unsure of the taxi route.
  • Check for traffic before crossing any runway hold line and before entering a taxiway.
  • Turn on aircraft lights and the rotating beacon or strobe lights while taxing.
  • When landing, clear the active runway as soon as possible, then wait for taxi instructions before further movement.
  • Study and use proper phraseology in order to understand and respond to ground control instructions.
  • Write down complex taxi instructions at unfamiliar airports.

Approximately three runway incursions occur each day at towered airports within the United States. The potential that these numbers present for a catastrophic accident is unacceptable. The following are examples of pilot deviations, operational incidents (OI), and vehicle (driver) deviations that may lead to runway incursions.

Pilot Deviations:

  • Crossing a runway hold marking without clearance from ATC
  • Taking off without clearance
  • Landing without clearance

Operational Incidents (OI):

  • Clearing an aircraft onto a runway while another aircraft is landing on the same runway
  • Issuing a takeoff clearance while the runway is occupied by another aircraft or vehicle

Vehicle (Driver) Deviations:

  • Crossing a runway hold marking without ATC clearance

According to FAA data, approximately 65 percent of all runway incursions are caused by pilots. Of the pilot runway incursions, FAA data shows almost half of those incursions are caused by GA pilots.

Causal Factors of Runway Incursions

Detailed investigations of runway incursions over the past 10 years have identified three major areas contributing to these events:

  • Failure to comply with ATC instructions
  • Lack of airport familiarity
  • Nonconformance with standard operating procedures

Clear, concise, and effective pilot/controller communication is paramount to safe airport surface operations. You must fully understand and comply with all ATC instructions. It is mandatory to read back all runway “hold short” instructions verbatim.

Taxiing on an unfamiliar airport can be very challenging, especially during hours of darkness or low visibility. A request may be made for progressive taxi instructions which include step by step taxi routing instructions. Ensure you have a current airport diagram, remain “heads-up” with eyes outside, and devote your entire attention to surface navigation per ATC clearance. All checklists should be completed while the aircraft is stopped. There is no place for non-essential chatter or other activities while maintaining vigilance during taxi. [Figure 1]

Aircraft Collision Avoidance
Figure 1. Heads-up, eyes outside

Runway Confusion

Runway confusion is a subset of runway incursions and often results in you unintentionally taking off or landing on a taxiway or wrong runway. Generally, you are unaware of the mistake until after it has occurred.

In August 2006, the flight crew of a commercial regional jet was cleared for takeoff on Runway 22 but mistakenly lined up and departed on Runway 26, a much shorter runway. As a result, the aircraft crashed off the end of the runway.

Causal Factors of Runway Confusion

There are three major factors that increase the risk of runway confusion and can lead to a wrong runway departure:

  • Airport complexity
  • Close proximity of runway thresholds
  • Joint use of a runway as a taxiway

Not only can airport complexity contribute to a runway incursion; it can also play a significant role in runway confusion. If you are operating at an unfamiliar airport and need assistance in executing the taxi clearance, do not hesitate to ask ATC for help. Always carry a current airport diagram and trace or highlight your taxi route to the departure runway prior to leaving the ramp.

If you are operating from an airport with runway thresholds in close proximity to one another, exercise extreme caution when taxiing onto the runway. Figure 2 shows a perfect example of a taxiway leading to multiple runways that may cause confusion. If departing on Runway 36, ensure that you set your aircraft heading “bug” to 360°, and align your aircraft to the runway heading to avoid departing from the wrong runway. Before adding power, make one last instrument scan to ensure the aircraft heading and runway heading are aligned. Under certain circumstances, it may be necessary to use a runway as a taxiway. For example, during airport construction some taxiways may be closed requiring rerouting of traffic onto runways. In other cases, departing traffic may be required to back taxi on the runway in order to utilize the full runway length.

Aircraft Collision Avoidance
Figure 2. Confusing runway/runway intersection
Since inattention and confusion often are factors contributing to runway incursion, it is important to remain extremely cautious and maintain situational awareness (SA). When instructed to use a runway as a taxiway, do not become confused and take off on the runway you are using as a taxiway.

ATC Instructions

Title 14 of the Code of Federal Regulations (14 CFR) part 91, section 91.123 requires you to follow all ATC clearances and instructions. Request clarification if you are unsure of the clearance or instruction to be followed. If you are unfamiliar with the airport or unsure of a taxi route, ask ATC for a “progressive taxi.” Progressive taxi requires the controller to provide step-by-step taxi instructions.

The final decision to act on ATC’s instruction rests with you. If you cannot safely comply with any of ATC’s instructions, inform them immediately by using the word “UNABLE.” There is nothing wrong with telling a controller that you are unable to safely comply with the clearance.

Another way to mitigate the risk of runway incursions is to write down all taxi instructions as soon as they are received from ATC. [Figure 3] It is also helpful to monitor ATC clearances and instructions that are issued to other aircraft. You should be especially vigilant if another aircraft has a similar sounding call sign so there is no mistake about who ATC is contacting or to whom they are giving instructions and clearances.

Aircraft Collision Avoidance
Figure 3. A sound practice is to write down taxi instructions from ATC

Read back your complete ATC clearance with your aircraft call sign. This gives ATC the opportunity to clarify any misunderstandings and ensure that instructions were given to the correct aircraft. If, at any time, there is uncertainty about any ATC instructions or clearances, ask ATC to “say again” or ask for progressive taxi instructions.

ATC Instructions – “Hold Short”

The most important sign and marking on the airport is the hold sign and hold marking. These are located on a stub taxiway leading directly to a runway. They depict the holding position or the location where the aircraft is to stop so as not to enter the runway environment. [Figure 4] For example, Figure 5 shows the holding position sign and marking for Runway 13 and Runway 31.

Aircraft Collision Avoidance
Figure 4. Do NOT cross a runway holding position marking without ATC clearance. If the tower is closed or you are operating from a non-towered airport, check both directions for conflicting traffic before crossing the hold position marking


Aircraft Collision Avoidance
Figure 5. Runway 13-31 holding position sign and marking located on Taxiway Charlie
When ATC issues a “hold short” clearance, you are expected to taxi up to, but not cross any part of the runway holding marking. At a towered airport, runway hold markings should never be crossed without explicit ATC instructions. Do not enter a runway at a towered airport unless instructions are given from ATC to cross, takeoff from, or “line up and wait” on that specific runway.ATC is required to obtain a read-back from the pilot of all runway “hold short” instructions. Therefore, you must read back the entire clearance and “hold short” instruction, to include runway identifier and your call sign.

Figure 6 shows an example of a controller’s taxi and “hold short” instructions and the reply from the pilot.

Aircraft Collision Avoidance
Figure 6. Example of taxi and “hold short” instructions from ATC to a pilot

ATC Instructions – Explicit Runway Crossing

As of June 30, 2010, ATC is required to issue explicit instructions to “cross” or “hold short” of each runway. Instructions to “cross” a runway are normally issued one at a time, and an aircraft must have crossed the previous runway before another runway crossing is issued. Exceptions may apply for closely spaced runways that have less than 1,000 feet between centerlines. This applies to all runways to include active, inactive, or closed. Figure 7 shows communication between ATC and a pilot who is requesting a taxi clearance. Extra caution should be used when directed by ATC to taxi onto or across a runway, especially at night and during reduced visibility conditions. Always comply with “hold short” or crossing instructions when approaching an entrance to a runway. Scan the full length of the runway and the final approaches before entering or crossing any runway, even if ATC has issued a clearance.

Aircraft Collision Avoidance
Figure 7. Communication between ATC and a pilot who is requesting taxi procedures

ATC Instructions – “Line Up and Wait” (LUAW)

ATC now uses the “line up and wait” (LUAW) instruction when a takeoff clearance cannot be issued immediately due to traffic or other reasons. The words “line up and wait” have replaced “position and hold” in directing you to taxi onto a runway and await takeoff clearance.

An ATC instruction to “line up and wait” is not a clearance for takeoff. It is only a clearance to enter the runway and hold in position for takeoff. Under LUAW phraseology, the controller states the aircraft call sign, departure runway, and “line up and wait.” Be aware that “traffic holding in position” will continue to be used to advise other aircraft that traffic has been authorized to line up and wait on an active runway. Pay close attention when instructed to “line up and wait,” especially at night or during periods of low visibility. Before entering the runway, remember to scan the full length of the runway and its approach end for other aircraft.

There have been collisions and incidents involving aircraft instructed to “line up and wait” while ATC waits for the necessary conditions to issue a takeoff clearance. An OI caused a 737 to land on a runway occupied by a twin-engine turboprop. The turboprop was holding in position awaiting takeoff clearance. Upon landing, the 737 collided with the twin-engine turboprop.

When ATC instructs you to “line up and wait,” they should advise you of any anticipated delay in receiving your takeoff clearance. Possible reasons for ATC takeoff clearance delays may include other aircraft landing and/or departing, wake turbulence, or traffic crossing an intersecting runway.

• If advised of a reason for the delay, or the reason is clearly visible, expect an imminent takeoff clearance once the reason is no longer an issue.

• If a takeoff clearance is not received within 90 seconds after receiving the “line up and wait” instruction, contact ATC immediately.

• When ATC issues “line up and wait” instructions and takeoff clearances from taxiway intersection, the taxiway designator is included.

Example – “N123AG Runway One-Eight, at Charlie Three, line up and wait.”
Example – “N123AG Runway One-Eight, at Charlie Three, cleared for takeoff.”

If LUAW procedures are being used and landing traffic is a factor, ATC is required to:

• Inform the aircraft in the LUAW position of the closest aircraft that is requesting a full-stop, touch-and-go, stop-and-go, option, or unrestricted low approach.

Example – “N123AG, Runway One-Eight, line up and wait, traffic a Cessna 210 on a six-mile final.”

• In some cases, where safety logic is being used, ATC is permitted to issue landing clearances with traffic in the LUAW position. Traffic information is issued to the landing traffic.

Example – “N456HK, Runway One-Eight, cleared to land, traffic a DeHavilland Otter holding in position.”

NOTE: ATC will/must issue a takeoff clearance to the traffic holding in position in sufficient time to ensure no conflict exists with landing aircraft. Prescribed runway separation must exist no later than when the landing aircraft crosses the threshold.

• In cases where ATC is not permitted to issue landing clearances with traffic in the LUAW position, traffic information is issued to the closest aircraft that is requesting a full-stop, touch-and-go, stop-and-go, option, or unrestricted low approach.

Example – “N456HK, Runway One-Eight, continue, traffic holding in position.”

ATC Instructions – “Runway Shortened”

You should review NOTAMs in your preflight planning to determine any airport changes that will affect your departure or arrival. When the available runway length has been temporarily or permanently shortened due to construction, the ATIS includes the words “warning” and “shortened” in the text of the message. For the duration of the construction when the runway is temporarily shortened, ATC will include the word “shortened” in their clearance instructions. Furthermore, the use of the term “full length” will not be used by ATC during this period of the construction.Some examples of ATC instructions are:

  • “Runway three six shortened, line up and wait.”
  • “Runway three six shortened, cleared for takeoff.”
  • “Runway three six shortened, cleared to land.”

When an intersection departure is requested on a temporarily or permanently shortened runway during the construction, the remaining length of runway is included in the clearance. For example, “Runway three six at Echo, intersection departure, 5,600 feet available.” If following the construction, the runway is permanently shortened, ATC will include the word “shortened” until the Chart Supplement U.S. (formerly Airport/Facility Directory) is updated to include the permanent changes to the runway length.

Pre-Landing, Landing, and After-Landing

While en route and after receiving the destination airport ATIS/landing information, review the airport diagram and brief yourself as to your exit taxiway. Determine the following:

  • Are there any runway hold markings in close proximity to the exit taxiway?
  • Do not cross any hold markings or exit onto any runways without ATC clearance.

After landing, use the utmost caution where the exit taxiways intersect another runway, and do not exit onto another runway without ATC authorization. Do not accept last minute turnoff instructions from the control tower unless you clearly understand the instructions and are at a speed that ensures you can safely comply. Finally, after landing and upon exiting the runway, ensure your aircraft has completely crossed over the runway hold markings. Once all parts of the aircraft have crossed the runway holding position markings, you must hold unless further instructions have been issued by ATC. Do not initiate non-essential communications or actions until the aircraft has stopped and the brakes set.