Taxiing (ASEL, AMEL)

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" (PHAK ch. 14). Approximately three runway incursions occur each day at towered airports in the United States. About 65 percent of all runway incursions are caused by pilots, and FAA data shows almost half of those pilot incursions are caused by GA pilots.

From detailed investigations over the past ten years:

• Failure to comply with ATC instructions
• Lack of airport familiarity
• Nonconformance with standard operating procedures (PHAK ch. 14)

Note that all three are addressable before the airplane moves — which is why CA.II.D.K6a makes flight deck activities prior to taxi, including route planning and Hot Spot identification, a knowledge element in its own right.

• Airport diagram out and in view at all times (AFH ch. 2), taxi route traced or highlighted before leaving the ramp
• Hot Spots identified — they're depicted on the airport diagram and described in the Chart Supplement; PHAK ch. 14 shows a runway/runway intersection at Sioux Gateway (SUX) designated HS1 as the type case
• NOTAMs reviewed for runway and taxiway closures and construction
• Expected route briefed against the expected departure runway, with the departure emergency plan attached to it
• Checklists finished stopped, and the sterile flight deck starts when the airplane starts moving

Read back your complete clearance with your aircraft call sign, so ATC can catch a misunderstanding and confirm it went to the right airplane. It is mandatory to read back all runway "hold short" instructions verbatim — the entire clearance and hold-short instruction, including runway identifier and your call sign — and ATC is required to obtain that read-back (PHAK ch. 14). Writing the instructions down is the FAA's own recommended practice at complex or unfamiliar airports.

Only on explicit instruction for that specific runway. PHAK ch. 14: "Do not enter a runway at a towered airport unless instructions are given from ATC to cross, take off from, or 'line up and wait' on that specific runway." A hold-short clearance means taxi up to, but not across any part of, the runway holding position marking. And you should never allow any part of the aircraft to cross a runway holding position sign — vertical or surface-painted — without a clearance.

Four yellow lines across the taxiway — two solid, two dashed, painted across the entire taxiway width and collocated with the holding position sign.

Approaching the runway: you see the two solid lines first — stop so that no portion of the aircraft intersects the first solid yellow line, and don't cross the double solid lines until ATC clears you.

Exiting the runway: you approach the double dashed lines — the entire aircraft must cross both the dashed and the solid lines to be clear of the runway, and no ATC clearance is needed to cross this marking when exiting (PHAK ch. 14).

No clearance exists to receive, so the clearing is yours. You may taxi onto or across the runway — past the runway holding position sign — only when the runway is clear of aircraft and there are no aircraft on final approach, and then with extreme caution, always looking both ways (PHAK ch. 14). Self-announce on CTAF, build a mental picture from other traffic's calls, and assume NORDO aircraft exist.

It's the human tendency to follow the same procedure over and over: a pilot given the same taxi instructions repeatedly "starts expecting those same instructions and might not realize that those instructions no longer apply. It only takes missing one instruction or turn to generate an accident" (AFH ch. 2). Defeat it mechanically, not by trying harder — write the clearance down every time, read back what was said rather than what you expected, and be especially vigilant when another aircraft has a similar-sounding call sign (PHAK ch. 14).

Stop the airplane clear of intersections and rebuild the plan before moving again: new route on the diagram, new Hot Spots, new hold-short points — then the takeoff data, because a different runway means different length, wind components, obstacles, and a different engine-failure plan. CA.II.D.R3 lists the route or runway change as a named risk precisely because the discarded old plan keeps running in the background. If it can't be done safely, "UNABLE" is a complete answer; 91.123 requires compliance with clearances, but the final decision to act on an instruction rests with you (PHAK ch. 14).

It's a subset of runway incursions in which you unintentionally take off from or land on a taxiway or the wrong runway, and you're generally unaware until after it has occurred. Three factors raise the risk (PHAK ch. 14):

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

In August 2006 the crew of a commercial regional jet cleared for takeoff on Runway 22 lined up and departed on Runway 26 — a much shorter runway — and crashed off the end.

Set the heading bug to the assigned runway heading — depart Runway 36, bug 360° — align the airplane with the runway, and make one last instrument scan to confirm aircraft heading and runway heading agree before adding power (PHAK ch. 14). The AFH says the same from the other direction: ensure that runway numbers on paved runways agree with the magnetic compass and heading indicator before beginning the takeoff roll (AFH ch. 2). And when instructed to use a runway as a taxiway, do not become confused and take off on it.

Slow enough that "movement of the airplane is dependent on the throttle" — that is, when the throttle is closed the airplane can be stopped promptly (AFH ch. 2). Speed is set with power, not brakes: other than sharp turns at low speed, the throttle should always be at idle before the brakes are applied, and taxiing with a power setting that requires the brakes to control speed is called out as a common error. Downwind, keep engine power to a minimum and apply brakes only occasionally to avoid overheating them.

Place the yellow centerline stripe under the center of the fuselage. Some taxiways have above-ground taxi lights and signage that can strike the airframe or propellers if control is sloppy (AFH ch. 2). Slow down before turns — sharp high-speed turns put side loads on the gear and can cause tire damage, an uncontrollable swerve, or a ground loop, and swerves are most likely when turning from a downwind heading toward an upwind heading. Stop with the nosewheel straight to relieve side load.

Quartering headwind: holding the upwind aileron up reduces the wind's lifting action on that wing, and the downwind aileron going down adds a little lift and drag on the far wing, further resisting the upwind wing rising. Quartering tailwind: elevator down and upwind aileron down reduce the wind's tendency to get under the tail and the wing and nose the airplane over (AFH ch. 2). In a tailwheel airplane the elevator is held full aft to keep the tail down, moving toward neutral only in a very strong headwind.

"The brakes should be tested for proper operation as soon as the airplane is put in motion" (AFH ch. 2, and CA.II.D.S5). Apply power to start moving slowly forward, retard the throttle, and apply just enough pressure to one side then the other to confirm both brakes function and react. If braking performance is unsatisfactory, the engine should be shut down immediately — you don't taxi toward a runway on brakes you don't trust.

A flight-instrument cross-check while the airplane is moving:

• Airspeed: at or near zero
• Attitude indicator: level in pitch and roll, no flags
• Altimeter: indicating field elevation within limits
• Turn indicator: correct direction of turn, ball moving toward the outside of the turn, no flags
• Directional gyro: set, cross-checked against the magnetic compass, agreeing with the direction of taxi
• VSI: reading zero

Works the same on mechanical instruments or glass (AFH ch. 2).

Everything gets slower and more deliberate, with the diagram in hand. The AFH's baseline lighting rule for ground operations: anti-collision lights on at all times before engine start, and for night operations the position (navigation) lights on as well (AFH ch. 2). The PHAK adds it to the incursion-avoidance list directly: turn on aircraft lights and the rotating beacon or strobe lights while taxiing (PHAK ch. 14). Courtesy still applies — don't blind the crew ahead of you while holding short.

Stop, tell ATC, and ask. The published answer is progressive taxi — a request that requires the controller to provide step-by-step taxi routing instructions — and the PHAK's advice for unfamiliar airports is not to hesitate to ask for help. If clearance from an object is ever in doubt, stop the airplane and check it; it may be necessary to have the airplane towed or moved by ground crew (AFH ch. 2). Guessing on a taxiway is how a pilot deviation becomes an incursion.

Read the visual wind indicators. The wind direction indicator can be a wind cone (wind sock), tetrahedron, or wind tee, usually in a central location near the runway and often at the center of a segmented circle, which identifies the traffic pattern direction when it is other than standard left-hand (PHAK ch. 14). Reading them:

• A wind sock extends straighter in strong winds and moves back and forth when the wind is gusting — it's the only one of the three that gives you velocity information
• A wind tee and a tetrahedron swing freely to align with the wind, but both can also be manually set to the runway in use — so cross-check the wind sock if one is available
• A tetrahedron indicates landing direction only, small end pointing the direction of landing; at towered airports reference it only when the tower is closed, because tower instructions supersede it
• The segmented circle also carries landing strip indicators (installed in pairs, showing landing strip alignment) and traffic pattern indicators (showing the turn direction where the pattern is non-standard)

Check the indicators even when a CTAF advisory gave you a wind — the PHAK's own caution is that there is no assurance the information provided is accurate.

Beyond hold position signs and markings:

• Surface painted holding position sign: white characters on a red background, left of the taxiway centerline
• Runway distance remaining signs: black background, white number = thousands of feet of landing runway remaining; the last sign, "1," is located at least 950 feet from the runway end
• ILS critical area holding position marking

LAHSO: as PIC you have the final authority to accept or decline, you must understand the reduced runway distance before accepting, and pilots should only receive a LAHSO clearance when there is a minimum ceiling of 1,000 feet and 3 statute miles visibility (PHAK ch. 14).