Airport Signs, Markings, and Lights

Airport signs use a fixed set of colors, and each color has one meaning. A red sign with white letters is a mandatory instruction sign. The AIM: "These signs have a red background with a white inscription and are used to denote: 1. An entrance to a runway or critical area; and 2. Areas where an aircraft is prohibited from entering." The most important mandatory sign is the runway holding position sign, "located at the holding position on taxiways that intersect a runway or on runways that intersect other runways." Its numbers match the direction of the runway: "'15-33' indicates that the threshold for Runway 15 is to the left and the threshold for Runway 33 is to the right" 1. A red sign means stop unless the pilot holds a clearance past it.

Location signs and direction signs

A black sign with yellow letters names the taxiway the airplane is on. The AIM says the taxiway location sign "has a black background with a yellow inscription and yellow border," and "the inscription is the designation of the taxiway on which the aircraft is located." A yellow sign with black letters and an arrow names an intersecting taxiway and the direction of the turn: "Direction signs have a yellow background with a black inscription. The inscription identifies the designation(s) of the intersecting taxiway(s) leading out of the intersection," and "each designation is accompanied by an arrow indicating the direction of the turn" 2. A black sign gives location and a yellow sign gives direction. A red sign gives a mandatory instruction.

Distance remaining

Runway distance remaining signs show the length of runway that remains. The AIM: they "have a black background with a white numeral inscription and may be installed along one or both side(s) of the runway. The number on the signs indicates the distance (in thousands of feet) of landing runway remaining. The last sign (i.e., the sign with the numeral '1') will be located at least 950 feet from the runway end" 3. A "3" means three thousand feet of runway remain. The pilot reads the signs on the takeoff roll and the landing rollout. A number smaller than the number in the briefing is a reason to stop.

The runway holding position marking is four yellow lines across the taxiway: two solid, two dashed. The AIM: "For runways, these markings indicate where aircraft MUST STOP when approaching a runway. They consist of four yellow lines, two solid and two dashed, spaced six or twelve inches apart, and extending across the width of the taxiway or runway. The solid lines are always on the side where the aircraft must hold" 4. The airplane holds on the solid side. On the dashed side the airplane is on the runway, and it crosses the lines to clear the runway.

Crossing the marking

The pilot crosses the marking at a towered airport on one condition. The AIM: "When approaching runways at airports with an operating control tower, pilots must not cross the runway holding position marking without ATC clearance." The clearance names that runway by number, and the pilot reads it back. At a non-towered airport the pilot looks for traffic: "Pilots approaching runways at airports without an operating control tower must ensure adequate separation from other aircraft, vehicles, and pedestrians prior to crossing the holding position markings." On leaving a runway, "an aircraft exiting a runway is not clear of the runway until all parts of the aircraft have crossed the applicable holding position marking" 4.

The pilot looks both ways down the runway and up final before crossing, at a towered or a non-towered airport. AC 91-73B recommends a reminder after the readback: "Given that many runway incursions occur even after the pilot reads back the 'hold short' instruction, pilots should develop a technique to remind themselves to 'hold short' of a hold line" 5.

Runway numbers

A runway's number is its magnetic heading, rounded to the nearest 10 degrees, with the last zero dropped. The AIM: "The runway number is the whole number nearest one-tenth the magnetic azimuth of the centerline of the runway, measured clockwise from the magnetic north" 6. Runway 31 points about 310 degrees magnetic. Runway 13 is the same pavement in the opposite direction. On the runway, the heading indicator must match the runway number. This check is the last check before the takeoff roll.

Displaced thresholds and chevrons

A displaced threshold puts the landing point farther down the runway. The AIM: "A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction." The markings are "white arrows ... along the centerline in the area between the beginning of the runway and displaced threshold" and a white bar 7. The pilot can taxi and take off on the area behind the bar. The pilot lands beyond the bar.

Chevrons mark pavement that is not for use. The AIM: "These markings are used to show pavement areas aligned with the runway that are unusable for landing, takeoff, and taxiing. Chevrons are yellow" 8. Blast pads and stopways carry them. Pavement with arrows is usable for taxi and takeoff. Pavement with chevrons is not usable for taxi, takeoff, or landing.

A taxiway carries "a single continuous yellow line, 6 inches (15 cm) to 12 inches (30 cm) in width," and the airplane "should be kept centered over this line during taxi. However, being centered on the taxiway centerline does not guarantee wingtip clearance with other aircraft or other objects." An enhanced centerline warns of a runway ahead: "The enhanced taxiway centerline marking consists of a parallel line of yellow dashes on either side of the normal taxiway centerline. The taxiway centerlines are enhanced for a maximum of 150 feet prior to a runway holding position marking. The purpose of this enhancement is to warn the pilot that he/she is approaching a runway holding position marking and should prepare to stop" 9. Dashes beside the line mean a runway is close. AC 91-73B states the difference between the two centerlines: "runways have white, segmented center lines, whereas taxiways have continuous, yellow center lines" 10. A white dashed line under the nose means the airplane is on a runway.

The ILS critical area

Some taxiways cross the ILS critical area, the ground area where the ILS signal forms. The marking there resembles a ladder: "Holding position markings for ILS critical areas consist of two yellow solid lines spaced two feet apart connected by pairs of solid lines spaced ten feet apart extending across the width of the taxiway." The sign beside it reads "ILS." The pilot holds at the marking only when ATC instructs: "When instructed by ATC to hold short of the ILS critical area, pilots MUST STOP so that no part of the aircraft extends beyond the holding position marking" 11. Without an instruction, the marking does not require a stop.

The flight of Comair 5191

On August 27, 2006, at 6:06 in the morning, Comair flight 5191 took off from the wrong runway at Blue Grass Airport, Lexington, Kentucky. The airplane, a Bombardier CRJ-100, ran off the end of the runway and hit a berm and the perimeter fence. It then hit trees and the ground. The captain, the flight attendant, and 47 passengers died. The first officer was seriously injured. It was night, and the weather was clear 12.

Blue Grass Airport had two runways that crossed. Runway 22, the air carrier runway, was 7,003 feet long with high intensity edge lights. Runway 26, the general aviation runway, was 3,501 feet long. It was restricted to daytime VFR use by airplanes under 12,500 pounds. Its edge lights were disconnected in 2001.

The airport was in the last weeks of a construction project. A local NOTAM closed taxiway A north of runway 26 a week before, and barricades blocked it. The airport renamed the old taxiway A5 as taxiway A. The Jeppesen chart in the cockpit did not show either change. Two regional jets taxied the same route to runway 22 and departed in the four minutes before Comair 5191 12.

The crew briefed runway 22 four times. The first officer, briefing the lights, said "lights are out all over the place," from a landing there two nights before. The tower's one controller cleared them to taxi to runway 22. Under the rules of the time, that clearance let them cross runway 26 without stopping. From 6:03:16 to 6:03:56, during the taxi, the crew talked about job opportunities.

At 6:04:33 the captain stopped at the hold short line for runway 26, 560 feet short of the hold short line for runway 22. The first officer told the tower they were ready "at his leisure." The controller said "fly runway heading, cleared for takeoff." Nobody said a runway number.

The captain taxied across the runway 26 hold short line and turned onto runway 26. He gave control of the airplane to the first officer. The heading bugs on both displays read 227 degrees, the heading of runway 22. The airplane pointed at 266 degrees.

At 6:06:16, rolling, the first officer said, "that is weird with no lights." The captain said, "yeah." The airplane hit the berm 265 feet past the end of runway 26 at 6:06:33, two seconds after the captain called rotate 12.

The NTSB found that "adequate cues existed on the airport surface and available resources were present in the cockpit to allow the flight crew to successfully navigate from the air carrier ramp to the runway 22 threshold." After the accident, investigators viewed the taxi route from a CRJ at night: "taxiway location signs were visible along the full length of the taxi route, a runway 26 holding position sign adjacent to the runway 26 hold short line was visible, and the runway 26 numbers were visible." The probable cause was "the flight crewmembers' failure to use available cues and aids to identify the airplane's location on the airport surface during taxi and their failure to cross-check and verify that the airplane was on the correct runway before takeoff," and two factors contributed. The factors were the nonpertinent conversation during taxi, and the FAA's failure to require an explicit clearance for each runway crossing 12.

Where the accident could have been prevented

An airline crew in an airline airplane took off from the wrong runway, and 49 people died. Each step below names the cue or the habit that would have prevented the accident, with its PAVE category.

The colors of the airport beacon show the kind of airport below. The AIM lists the colors: "White and Green- Lighted land airport. Green alone- Lighted land airport. White and Yellow- Lighted water airport." A military airport beacon also flashes white and green, but is "differentiated from civil beacons by dualpeaked (two quick) white flashes between the green flashes" 13. Two white flashes and a green flash mean a military airport.

A beacon that runs in daylight is a caution. The AIM: "In Class B, Class C, Class D and Class E surface areas, operation of the airport beacon during the hours of daylight often indicates that the ground visibility is less than 3 miles and/or the ceiling is less than 1,000 feet." The AIM adds the limit: "Pilots should not rely solely on the operation of the airport beacon to indicate if weather conditions are IFR or VFR," and "there is no regulatory requirement for daylight operation" 14. Many beacons run on a photocell or a clock. The pilot decides from the weather report, not from the beacon.

Runway lights

Runway edge lights are white. The AIM: "The runway edge lights are white, except on instrument runways yellow replaces white on the last 2,000 feet or half the runway length, whichever is less, to form a caution zone for landings." The lights at the runway ends show a different color in each direction: "The lights marking the ends of the runway emit red light toward the runway to indicate the end of runway to a departing aircraft and emit green outward from the runway end to indicate the threshold to landing aircraft" 15. Green lights ahead on final mark the threshold. Red lights ahead on the takeoff roll mark the end of the pavement. Runway 26 at Lexington had its edge lights disconnected.

Taxiway lights

Taxiway edge lights "emit blue light." Taxiway centerline lights, where installed, "are steady burning and emit green light" 16. The edges are blue and the centerline is green. A runway has white edges and no blue. At night, blue on both sides means a taxiway, and white on both sides means a runway.

The VASI shows the glidepath in two colors. The AIM: "The basic principle of the VASI is that of color differentiation between red and white. Each light unit projects a beam of light having a white segment in the upper part of the beam and red segment in the lower part of the beam" 17.

The pilot reads the two bars as the far bar over the near bar. Red over white is on the glidepath. White over white is above it. Red over red is below it. The memory aid is red over white, you are all right. The pilot begins the descent on the VASI only when the airplane is "visually aligned with the runway" 17.

PAPI

The PAPI puts the same lights in one row. The AIM: it "uses light units similar to the VASI but are installed in a single row of either two or four light units," and "the row of light units is normally installed on the left side of the runway" 18. With four lights, two white and two red is on the 3-degree path. Three or four white is high. Three or four red is low. More white lights mean the airplane is higher, and more red lights mean the airplane is lower.

Pilot-controlled lighting

At many airports the pilot turns the lights on from the air. The AIM: "Radio control of lighting is available at selected airports to provide airborne control of lights by keying the aircraft's microphone." The Chart Supplement "contains the types of lighting, runway and the frequency that is used to activate the system." The AIM's table gives the clicks: "7 times within 5 seconds, Highest intensity available; 5 times within 5 seconds, Medium or lower intensity; 3 times within 5 seconds, Lowest intensity available." The lights stay on for a fixed period: "All lighting is illuminated for a period of 15 minutes from the most recent time of activation." The AIM's advice is to "always initially key the mike 7 times," then reduce, and to key again "just prior to entering the final segment of an approach" so that the full 15 minutes are available 19.

REIL

Runway end identifier lights are two flashing lights at the threshold. The AIM: "The system consists of a pair of synchronized flashing lights located laterally on each side of the runway threshold," effective for "identification of a runway surrounded by a preponderance of other lighting" 20. Their purpose is to make the runway end visible among the other lights around it.

The pilot plans the taxi before the airplane moves. AC 91-73B: "Review the current airport diagram and hot spots and, if in use, a published textual description of standard taxi routes to provide an overall 'big picture' of the airport and its potential areas for a runway incursion." The briefing covers "the expected taxi route to include any hold short lines and runways to cross, hot spots, as well as any other potential conflicts" 21. Hot spots are the circled places on the diagram where the risk of a runway incursion is known to be higher. The pilot draws or speaks the route and names each hold short line.

NOTAMs

The pilot reads the NOTAMs before taxi. The AIM: "The NOTAM system provides pilots with time critical aeronautical information that is temporary." NOTAMs cover "Runways, taxiways, and ramp restrictions" and "Obstructions" 22. Each of these is in a NOTAM and not on the diagram:

• a closed taxiway
• a closed runway
• an unlit tower
• construction beside the route.

AC 91-73B: "If a clearance is received to use a runway/taxiway that a NOTAM/ATIS broadcast indicates is closed, query the controller for verification of clearance" 23. The diagram shows the airport at the date of the chart. The NOTAMs show the airport today.

The wind indicators

The pilot reads the windsock and the tetrahedron before each takeoff and landing. The windsock hangs from a pole, and its small end points away from the wind: "the large end of the wind cone/wind sock points into the wind" 24. The Pilot's Handbook says the sock "allows the pilot to estimate the wind velocity and/or gust factor," and that tetrahedrons "can swing freely and align themselves with the wind direction" 25. A tetrahedron shows landing direction: "The small end of the tetrahedron points in the direction of landing," and the pilot must not use it "for any purpose other than as an indicator of landing direction" 26. The sock shows the wind. The tetrahedron shows the landing runway.

Airplane lights on the ground

Section 91.209 sets two rules. The first rule, from sunset to sunrise, is that a pilot must not "operate an aircraft unless it has lighted position lights," and the second rule applies at any hour. Under the second rule a pilot must not "operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights," except when the pilot in command decides that turning them off "would be in the interest of safety" 27. The practice is:

• beacon on whenever the engine runs
• position lights on from sunset to sunrise
• strobes off on the ramp when they would affect the vision of a nearby pilot, and on for the runway.

AC 91-73B: "Strobe lights should not be illuminated if they will adversely affect the vision of other pilots." For an airplane lined up and waiting on the runway at night, the AC suggests "lining up slightly (approximately 3 feet) to the left or right of the centerline (CL) to enable a landing aircraft to visually differentiate your aircraft from the runway lights" 28.

At night and in low visibility the pilot taxis slower. AC 91-73B: "Any time the pilot is uncertain of their location on the airport or during taxi, do not stop on a runway. Stop the aircraft and immediately advise ATC, and, if necessary, request progressive taxi instructions" 10. In progressive taxi, the controller gives one turn at a time. Where green centerline lights exist, the pilot follows them. The AC states: "Pilots should be especially vigilant when instructed to LUAW, particularly at night or during periods of reduced visibility" 5. The pilot stops the airplane as soon as its position is uncertain, anywhere except on a runway.

Heads-down tasks

Heads-down tasks are:

• programming
• checklists
• messages.

The pilot does each with the airplane stopped. AC 91-73B: "it is extremely important that pilots perform all heads-down tasks (e.g., programming the FMS and calculating takeoff data) while the aircraft is stopped so they can maintain outside vigilance and SA" 29. The pilot stops clear of the movement area or at a place the controller has given. The pilot watches outside while the airplane moves.

The incursion defense

The defense against a runway incursion is four actions on each taxi:

• know where the airplane is, from the signs and the diagram
• know where ATC has cleared it to, from the readback
• read back each instruction that names a runway, with the runway number and the call sign
• never cross a red sign, a holding position marking, or red lights without resolving the doubt.

The AIM states the fourth action as a rule: at a towered airport, "pilots must not cross the runway holding position marking without ATC clearance" 4. The pilot stops and asks to resolve the doubt.

Expectation bias

A pilot who taxied a route yesterday expects the same route today and can mishear today's clearance as yesterday's route. AC 91-73B: "A potential pitfall of pretaxi and prelanding planning is setting expectations and then receiving different instructions from ATC. Pilots need to follow the clearance or instructions that are actually received, and not the ones they expected to receive." The defense is a written clearance: "Written taxi instructions can be used as a reference for reading back the instructions to ATC and for maintaining SA" 30. The pilot writes the clearance down and reads it back from the paper. The pilot then follows the paper, not memory.

The Comair crew expected runway 22 and briefed runway 22. They taxied onto runway 26 with the sign for runway 26 beside them.

Ramp security

Security on the ramp is part of ground operations. AOPA and the TSA run Airport Watch: "AOPA partnered with the TSA to develop a nationwide Airport Watch Program that uses the more than 650,000 pilots as eyes and ears for observing and reporting suspicious activity." The number is 866-GA-SECURE: "Since December 2002, a toll-free national government hotline (1/866-GA-SECURE, or 1/866-427-3287), has been in operation as part of the Aircraft Owners and Pilots Association's (AOPA's) Airport Watch program" 31. The practices are:

• use the airplane's door locks whenever the airplane is unattended, and consider auxiliary locks
• lock hangar doors and close security gates behind you
• keep the ignition keys separate from the airplane
• report anyone "attempting to access an aircraft by force, without keys, or using tools such as crowbars or screwdrivers," and "individuals unfamiliar with aviation procedures who appear to be inspecting or attempting to operate an aircraft."

The pilot ties down and locks a parked airplane. The pilot questions or reports a person near an airplane who has no reason to be there.