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Taxiing

Introduction:

  • Having just started the aircraft and completed the required checklists, the pilot is ready to put the aircraft in motion
  • Taxiing is that movement of an aircraft while on the ground, under its own power
  • Taxiing is accomplished primarily through the use of the rudder and brakes however, pilots are also required to mitigate the impacts of wind
  • Since movement on an airport's surface involves coordination, clearances requirements/coordination are required to operate
  • With the basics in mind, pilots execute Taxi Procedures as they move about an airport's surface area
  • While the movement of the aircraft is our primary concern, there remain some checklist items we must accomplish to prepare/close-out an operation
  • Finally, while taxiing seems straight forward, it can also be an art, with best practices that can help pilots
  • Once your engine has started you must be aware of what you're doing and keep a visual scan, your "flight" has begun
    • It may be required initially to tow the aircraft before engines are started to be safe

Steering and Braking:

  • Steering is accomplished with rudder pedals and brakes
    • The pilot applies the rudder in the desired direction of turn and use the appropriate power or brake to control the taxi speed
    • To tighten the turn after full pedal deflection is reached, the brake may be applied as needed
  • When first beginning to taxi, conduct a check of braking effectiveness
    • Release the brakes, and add power as required to allow the airplane to begin moving forward
    • Reduce the power to idle and depress the top portion of one side, then the other, to confirm proper function and reaction of both brakes
      • Be mindful of the area around you (in front, behind, and to the sides), especially if you're in a congested ramp
        • Checking brakes individually is ideal, but checking them together, if required, will suffice
      • Apply pressure sufficiently enough to cause the airplane to abruptly dip, or to a full stop if desired
    • If unsatisfactory, bring the airplane to a stop and consider taxi maneuvers (such as a loop) to maintain position on the airfield
  • To verify steering, depress the rudder pedal in the direction of turn desired
    • Verify that the airplane responds properly to the rudder pedal input
  • Make sure to check the braking and steering for each position that may need to use them (i.e., both seats)
  • More engine power may be required to start the airplane moving forward, or to start a turn, than is required to keep it moving in any given direction
    • When using additional power, the throttle should immediately be retarded once the airplane begins moving to prevent excessive acceleration
  • Stopping:
    • The rudder pedal should be held in the direction of the turn until just short of the point where the turn is to be stopped
      • Rudder pressure is then released or opposite pressure is applied as needed
    • When stopping the airplane, it is advisable to always stop with the nosewheel straight ahead to relieve any side load on the nosewheel and to make it easier to start moving ahead
    • During crosswind taxiing, even the nosewheel-type airplane has some tendency to weathervane
    • However, the weathervaning tendency is less than in tailwheel-type airplanes because the main wheels are located behind the airplane's center of gravity, and the nosewheel's ground friction helps to resist the tendency
    • The nosewheel linkage from the rudder pedals provides adequate steering control for safe and efficient ground handling, and normally, only rudder pressure is necessary to correct for a crosswind
    • Downwind taxiing usually requires less engine power after the initial ground roll is begun, since the wind is pushing the airplane forward
    • To avoid overheating the brakes and controlling the airplane's speed when taxiing downwind, the pilot must keep engine power to a minimum
      • Rather than continuously riding the brakes to control speed, it is appropriate to apply brakes only occasionally
      • Avoid resting toes on the brakes, resulting in unnecessarily dragging the brakes
      • Other than sharp turns at low speed, the throttle should always be at idle before the brakes are applied

Wind Impacts on Taxi:

  • When taxiing at appropriate speeds in no-wind conditions, the aileron and elevator control surfaces have minimal effect on directional control of the airplane
    • These controls should not be considered steering devices and should be held in a neutral position
  • The presence of moderate to strong winds and/or a strong propeller slipstream makes use of the aileron and elevator necessary to maintain control of the aircraft's roll/pitch while taxiing
  • This becomes apparent when considering the lifting action that may be created on the horizontal tail surfaces by either of those two factors
  • Elevator Usage:

    • The elevator control in nosewheel-type airplanes should be held in the neutral position, while in tailwheel-type airplanes, it should be held in the full aft position to hold the tail down
    • When taxiing with a quartering tailwind, the elevator should be held in the DOWN position, and the upwind aileron, DOWN
    • Since the wind is striking the airplane from behind, these control positions reduce the tendency of the wind to get under the tail and the wing and to nose the airplane over
  • Aileron Usage:

    • When taxiing with a quartering headwind, the wing on the upwind side (the side that the wind is coming from) tends to be lifted by the wind unless the aileron control is held in that direction (upwind aileron UP)
    • Moving the aileron into the UP position reduces the effect of the wind striking that wing, thus reducing the lifting action
    • This control movement also causes the downwind aileron to be placed in the DOWN position, thus a small amount of lift and drag on the downwind wing, further reducing the tendency of the upwind wing to rise

Clearance Requirements:

  • Clearances are required prior to moving an aircraft or vehicle onto the movement area during the hours an Air Traffic Control Tower (ATCT) is in operation
  • The movement area is normally described in local bulletins issued by the airport manager or air
    • These bulletins may be found in FSSs, fixed base operators offices, air carrier offices, and operations offices
  • A clearance must be obtained prior to taxiing on a runway, taking off, or landing during the hours an Airport Traffic Control Tower is in operation
  • When assigned a takeoff runway, ATC will first specify the runway, issue taxi instructions, and state any hold short instructions or runway crossing clearances if the taxi route will cross a runway
    • This does not authorize the aircraft to "enter" or "cross" the assigned departure runway at any point
    • In order to preclude misunderstandings in radio communications, ATC will not use the word "cleared" in conjunction with authorization for aircraft to taxi
  • ATC will issue an explicit clearance for all runway crossings
  • If a pilot is expected to hold short of a runway approach/departure (Runway XX APPCH/Runway XX DEP) hold area or ILS holding position (see FIG 2-3-15, Taxiways Located in Runway Approach Area), ATC will issue instructions
  • Relaying an ATC Clearance:

    • ARTCC clearances are relayed to pilots by airport traffic controllers in the following manner
      • Tower: "Beechcraft One Three One Five Niner, cleared to the Chicago Midway Airport via Victor Eight, maintain eight thousand"
      • Aircraft: "Beechcraft One Three One Five Niner, cleared to the Chicago Midway Airport via Victor Eight, maintain eight thousand"
    • Normally, an ATC IFR clearance is relayed to a pilot by the ground controller. At busy locations, however, pilots may be instructed by the ground controller to "contact clearance delivery" on a frequency designated for this purpose
    • No surveillance or control over the movement of traffic is exercised by this position of operation

Taxi Checklists:

  • Taxiing checklists are sometimes specified by the AFM/POH, and the pilot must accomplish any items that are required
  • If there are no specific checklist items, taxiing still provides an opportunity to verify the operation and cross-check of the flight instruments
    • The airspeed indicator should read at or near zero (depending on taxi speed, wind speed and direction, and lower limit sensitivity
    • The attitude indicator should indicate no more than 5° bank and relatively level pitch (depending on airplane attitude), with no flags
    • The altimeter should indicate the proper elevation within prescribed limits
    • The turn indicator should show the correct direction of turn with the ball movement toward the outside of the turn with no flags
    • The directional gyro should be set and crossed checked to the magnetic compass and verified accurate to the direction of taxi
    • The vertical speed indicator should read zero
  • These checks can be accomplished on conventional mechanical instrumented aircraft or glass cockpits
  • Do not perform any items while taxiing that prevent you from safely operating the aircraft

Taxi Procedures:

  • Taxi For Takeoff:

    1. Complete all checklists required before taxi
    2. Listen to ATIS/AWOS/ASOS, as appropriate
    3. Contact Clearance Delivery, as appropriate
    4. Contact Ground Control or CTAF, as appropriate:
      • State your aircraft identification, location, type of operation planned (VFR or IFR), if IFR, the point of first intended landing, if VFR, the cardinal direction, and that you have the appropriate ATIS/AWOS/ASOS code:
        • Pilot: "[Agency] Ground, [Callsign], [Location], [Operation] with [Information]"
        • Pilot" "Washington ground, Beechcraft One Three One Five Niner at hangar eight, ready to taxi, I-F-R to Chicago, with information Alpha"
    5. Ground will respond with your instructions:
      • ATC will first specify the runway, issue taxi instructions, and then state any required hold short instructions
      • "Taxi to" means you are cleared to cross all taxiways and runways excepting the assigned takeoff runway
      • "Hold short" means you cannot cross said runway or taxiway until cleared
      • ATC is required to issue "hold shorts" or "cleared to cross" on any runway active or not in between you and your destination
        • Ground: "Beechcraft one three one five niner, Washington ground, runway two seven, taxi via taxiways Charlie and Delta, hold short of runway three three left"
    6. Acknowledge the taxi clearance:
      • When taxi instructions are received from the controller, pilots should always read back:
        • Runway assignment
        • Any clearance to enter a specific runway
        • Any instruction to hold short of a specific runway or line up and wait

        • Controllers are required to request a read-back of runway hold short assignment when it is not received from the pilot/vehicle
      • Aircraft: "Beechcraft One Three One Five Niner, runway two seven, hold short of runway three three left"
      • The control tower also issues bulletins describing areas where they cannot provide service due to non-visibility or other reasons
        • This is usually done through ATIS/AWOS remarks
    7. Begin taxi, monitoring ground frequency until into the run-up area
    8. Check the heading indicator to ensure the reading has not precessed more than 3° in 15 minutes
  • Taxiing after Landing:

    • Exit the runway without delay, at the first available taxiway, or as instructed
      • All parts of the aircraft must be across the hold short line to be considered off the runway
    • Contact ground when directed by tower
  • Taxiing for Reasons Other Than Takeoff or Landing:

    • When issuing taxi instructions to any point other than an assigned takeoff runway, ATC will specify the point to taxi to, issue taxi instructions, and state any hold short instructions or runway crossing clearances if the taxi route will cross a runway
      • ATC is required to obtain a read-back from the pilot of all runway hold short instructions

Taxi Fundamentals/Operating Practices:

  • Hand-held Scanner
    Hand-held Scanner
  • An essential requirement in conducting safe taxi operations is where the pilot maintains situational awareness
  • Depending on the airport, parking, ramp, and taxiways may or may not be controlled
  • Taxi Planning Best Practices:

    • The pilot should make themselves familiar with the parking, ramp, and taxi environment
      • Especially at unfamiliar airports, review, and have available the airport diagram to maintain situational awareness
      • If routing is expected to be complex, consider listening to ground control, if able, on liveATC.net or with the use of a handset
    • The pilot must be vigilant of the entire area around the airplane to ensure that the airplane clears all obstructions
      • If, at any time, there is doubt about a safe clearance from an object, the pilot should stop the airplane and check the clearance
      • It may be necessary to have the airplane towed or physically moved by a ground crew
    • When taxiing, the pilot's eyes should be looking outside the airplane scanning from side to side while looking both near and far to assess routing and potential conflicts
      • It is helpful to use callouts to accomplish this task: "Cleared left, forward and right, going [Left/Forward/Right]"
    • A safe taxiing speed must be maintained
      • The primary requirements for safe taxiing are positive control, the ability to recognize any potential hazards in time to avoid them, and the ability to stop or turn where and when desired, without undue reliance on the brakes
    • The pilot should accurately place the aircraft centered on the taxiway at all times
      • Some taxiways have above ground taxi lights and signage that could impact the airplane or propellers if the pilot does not exercise accurate control
    • When taxiing, the pilot must slow down before attempting a turn
      • Sharp high-speed turns place undesirable side loads on the landing gear and may result in tire damage or an uncontrollable swerve or a ground loop
      • Swerves are most likely to occur when turning from a downwind heading toward an upwind heading
      • In moderate to high-wind conditions, the airplane may weathervane increasing the swerving tendency
  • Good operating practice dictates that pilots acknowledge all runway crossing, hold short, or takeoff clearances unless there is some misunderstanding, at which time the pilot should query the controller until the clearance is understood
    • NOTE: Air traffic controllers are required to obtain from the pilot a read-back of all runway hold short instructions
  • Pilots operating a single pilot aircraft should monitor only assigned ATC communications after being cleared onto the active runway for departure. Single pilot aircraft should not monitor other than ATC communications until flight from Class B, Class C, or Class D surface area is completed. This same procedure should be practiced from after receipt of the clearance for landing until the landing and taxi activities are complete. Proper effective scanning for other aircraft, surface vehicles, or other objects should be continuously exercised in all cases
  • At those airports where the U.S. Government operates the control tower and ATC has authorized noncompliance with the requirement for two-way radio communications while operating within the Class B, Class C, or Class D surface area, or at those airports where the U.S. Government does not operate the control tower and radio communications cannot be established, pilots must obtain a clearance by visual light signal prior to taxiing on a runway and prior to takeoff and landing
  • Upon reaching an intersection, you should get in the habit of telling yourself (or say allowed if with others) that the area is cleared
    • ICS: "Cleared left, forward and right, going [Left/Forward/Right]"
  • If leaning the mixture, do so enough to keep the engine running, but not so little so that if you push the throttle to full, you instead cause the engine to quit, vice take off lean
  • Taxi Speed:

    • Taxi speed is not specifically regulated; however, common sense must apply so as not to operate in a careless or reckless manner (FAR 91.13)
      • You should never taxi any faster than one can walk in the line
      • While on a taxiway, you should not taxi faster than one can jog
      • When entering a turn, be mindful of the stress you are placing on the gear as you turn and slow down
      • Care must be exercised when taxiing at night, in low visibility, or toward the sun to remain situational awareness as to where you are
        • This means half the speed and twice the caution
  • Compensating for Airport Slopes:

    • Runways are generally flat surfaces however small changes in elevation will impact the speed at which the aircraft moves
      • You will require more power uphill and less downhill
      • Every turn you make will impact the amount of power required to some degree
      • It is unlikely however, that you'll need to adjust than around 100 RPM to overcome to effects of slope
  • Compensating for Wind during Taxi:

    • Crosswinds can effect an aircraft, even when moving at slower speeds on the ground during taxi
    • Moderate to strong headwinds and/or a strong propeller slipstream makes the use of the elevator sometimes necessary to control pitch
    • Downwind taxiing will usually require less power and may require none, but do not ride the brakes
    • The upwind wing will tend to be lifted by the wind unless the aileron control is held in that direction
    • Weathervaning may occur as the wind effects a large portion of the aircrafts side [Figure 4]
      • This is more apparent in a tail wheel aircraft given the wheel is farther behind the center of gravity and comparatively farther from the main gear
    • The aileron and elevator should be positioned in such a way as to prevent undesirable effects on the aircraft
      • Remember the memory aid to: dive away and fly into the wind
        • The elevator must be neutral (for tricycle gear airplanes) or up (for tailwheel airplanes)
      • Remember also that turns will require change the direction the wind is coming from relative to the aircraft, requiring a change in control positions

Technique:

  • It will require a large amount of power to initially move the aircraft
    • As the aircraft starts to move, power must be retarded, possibly as far back as idle, to prevent continued acceleration
  • Steer with rudders, keeping your feet over, but not on, the breaks
  • Riding the brakes will reduce their lifespan and could render them less effective
    • Many high performance aircraft can produce enough thrust that riding the brakes may be necessary to keep the aircraft from speeding up; brake judiciously
  • Airplane Flying Handbook, Quartering Tailwind
    Airplane Flying Handbook,
    Quartering Tailwind
  • Jet aircraft can be dangerous when exhaust is swept across an area
  • Reduce the power to idle in a turn, but remember an aircraft stopped in a turn takes a lot of power to get moving again
    • Always execute good "tail pipe courtesy"

Taxi Operations During Low Visibility:

  • Pilots and aircraft operators should be constantly aware that during certain low visibility conditions the movement of aircraft and vehicles on airports may not be visible to the tower controller
    • This may prevent visual confirmation of an aircraft's adherence to taxi instructions
  • If pilots become disoriented, it is vitally important to notify the controller immediately
    • Pilots should proceed with extreme caution when taxiing toward the sun
    • When vision difficulties are encountered pilots should immediately inform the controller
  • Advisory Circular 120-57, Low Visibility Operations Surface Movement Guidance and Control System, commonly known as LVOSMGCS (pronounced "LVO SMIGS") describes an adequate example of a low visibility taxi plan for any airport which has takeoff or landing operations in less than 1,200 feet runway visual range (RVR) visibility conditions. These plans, which affect aircrew and vehicle operators, may incorporate additional lighting, markings, and procedures to control airport surface traffic. They will be addressed at two levels; operations less than 1,200 feet RVR to 500 feet RVR and operations less than 500 feet RVR
    • Specific lighting systems and surface markings may be found in Paragraph 2-1-11, Taxiway Lights, and Paragraph 2-3-4, Taxiway Markings
  • When low visibility conditions exist, pilots should focus their entire attention on the safe operation of the aircraft while it is moving. Checklists and nonessential communication should be withheld until the aircraft is stopped and the brakes set

Progressive Taxi:

  • If the pilot is unfamiliar with the airport or for any reason confusion exists as to the correct taxi routing, a request may be made for progressive taxi instructions which include step-by-step routing directions
  • Progressive instructions may also be issued if the controller deems it necessary due to traffic or field conditions (for example, construction or closed taxiways)
  • The need for progressive taxi can be mitigated by proper preflight planning and having airport diagrams handy

Regulation:

  • Taxi/landing lights shall be utilized to the maximum extent possible at night except to avoid blinding another pilot
    • The use of takeoffs-and-landings/taxi lights is an effective means of illuminating surface hazards during taxi movements at night and alerting all concerned of an aircraft's presence/position in flight
  • FAR 91.209 has specific guidance as to lighting requirements
Airplane Flying Handbook, Crosswind Taxiing Technique
Airplane Flying Handbook, Crosswind Taxiing Technique
Airplane Flying Handbook, Downwind Taxi
Airplane Flying Handbook,
Downwind Taxi
Airplane Flying Handbook, Quartering Headwind
Airplane Flying Handbook,
Quartering Headwind

Communications:

  • A low visibility taxi plan will exist giving the pilot additional instructions when the RVR is less than 1,200' and again in operations less than 600' RVR
  • Do not switch frequencies while taxiing, in case ground needs to contact you
  • Auto-switch tower when approaching the hold short to monitor traffic
  • If you have just cleared a runway and are looking to taxi, call with intentions as appropriate
    • ATC: "[Agency] Ground, [Callsign], clear of [Runway] at [Location], taxi to [Location]"
Airplane Flying Handbook, Surface Area Most Affected By Wind
Airplane Flying Handbook,
Surface Area Most Affected By Wind

Exiting the Runway:

  • Exit without delay at the first available taxiway or as instructed
  • All parts of the aircraft must be across the hold short line to be considered off the runway
  • Contact ground when directed by tower

Dangers:

  • Personnel must always be aware of the dangers associated with moving surfaces
  • Rotor wash created by the blades of a rotary-winged aircraft or thrust from the exhaust section of a fixed-winged aircraft may cause severe personnel injury
  • The proper safety equipment must always be worn when working on flight decks and flight lines
  • IT IS THE PILOT'S RESPONSIBILITY TO SEE AND AVOID ON THE TAXIWAY AS WELL


Tailwheel Considerations:

  • Aircraft with conventional landing gear (tailwheel/draggers) aircraft have special considerations that are unique to them
  • Ground Loop:

    • The center of gravity of a tailwheel aircraft is behind the cockpit which can cause instability during taxi
    • Make smooth inputs on the controls and be mindful that the center of gravity is not allowed to get to the side of the aircraft with enough momentum to carry it around
    • Once a ground loop has started there is no way to get out of it until it has run its course
    • In the interest of avoiding obstacles or staying on a paved surface however, differential breaking with the inside break will tighten the loop
  • Taxi Speed:

    • While speed can be a contributing factor to ground loops, it is also necessary to maintain positive control
    • If the aircraft is taxiing too fast, and breaks are applied too firmly, the tail can raise causing the tailwheel to lose effectiveness while simultaneously causing the propeller to move closer to the ground
    • If the tail comes up high enough, the pilot may experience a propeller, or "prop" strike

Hand Signals:

  • Airplane Flying Handbook, Standard Hand And Arm Signals
    Airplane Flying Handbook,
    Standard Hand And Arm Signals
  • Flight Personnel are utilized on many aircraft ramps to direct traffic in an orderly fashion in accordance with local procedures
  • Flashing your landing/taxi lights at the marshaller will help signal to them when you are ready, especially at night
    • Likewise, don't blind them with the light, turn it off until clear of the marshaller
  • General Signals:

    • Affirmative:

      • Day: Thumbs up or head nod
      • Night: Flashlight moved vertically up-and-down repeatedly
    • Negative:

      • Day: Thumbs down or head shake
      • Night: Flashlight moved horizontally back-and-forth repeatedly
    • All Clear (O.K.):

      • Day: One arm pointing up with the other pointing down
      • Night: Same signal as day, but with lights
    • Start Engine:

      • Day: Point to engine OR indicate engine number with fingers while making horizontal circular motion above head with other
      • Night: Same signal as day, but with lights
    • Proceed Straight Ahead:

      • Day: Hands gesture to come closer
      • Night: Same signal as day, but with lights
    • Pull Chocks:

      • Day: Move arms outward with thumbs pointed outward
      • Night: Same signal as day, but with lights
    • Turns:

      • Day: The direction of turn is indicated by that arm pointing downward while the other gestures to come closer
      • Night: Same signal as day, but with lights
    • Flagman Directs Pilot:

      • Day: Flagman holds hands in air to catch the pilot's attention
      • Night: Same signal as day, but with lights
    • Slow Down:

      • Day: With palms facing down, arms are moved up and down at side
      • Night: Same signal as day, but with lights
    • Insert Chocks:

      • Day: Move arms inward with thumbs pointed inward
      • Night: Same signal as day, but with lights
    • Cut Engine:

      • Day: A cutting motion with a flat palm is made across neck
      • Night: Same signal as day, but with lights
    • Stop:

      • Day: Arms are crossed with closed fist
      • Night: Same signal as day, but with lights
    • Clarify:

      • Day: Hand cupped behind ear as if listening
      • Night: None
    • Wait:

      • Day: Hand held up, palm toward pilot
      • Night: None
    • Ignore Last Signal:

      • Day: Hand waved back and forth in an erasing motion in front of face, with palm turned forward
      • Night: Trace of letter N, given by external light
    • Numbers:

      • Day:
        • Fingers held vertically indicate 1 through 5
        • Fingers held horizontally indicate 6 through 9
        • A clenched fist indicates zero
      • Night: None
  • Airplane Flying Handbook, Standard Hand And Arm Signals
    Airplane Flying Handbook,
    Standard Hand And Arm Signals

Taxiing Common Errors:

  • Forgetting to remove a tie-down or chocks prior to attempting movement
  • Improper aileron deflection, particularly after turning
  • Taxiing with a power setting that requires controlling taxi speed with the brakes

Case Studies:

  • NTSB Identification: MIA01LA034 The National Transportation Safety Board determines the probable cause(s) of this accident to be: The student pilot's failure to maintain a visual look out while transitioning from the active runway to a taxiway resulting in an on-ground collision with a taxiway sign

Conclusion:

  • Taxiing is part of every flight, and it should be part of planning
  • ATC clearances or instructions pertaining to taxiing are predicated on known traffic and known physical airport conditions
    • Since "the pilot-in-command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft" the pilot should obtain clarification of any clearance or instruction which is not understood
  • Therefore, it is important that pilots clearly understand the clearance or instruction
  • Although an ATC clearance is issued for taxiing purposes, when operating in accordance with the CFRs, it is the responsibility of the pilot to avoid collision with other aircraft
  • Be familiar with and comply with all airport markings and signs
    • Pay attention when in a movement area and be cognizant of expectation bias, that is having a belief you are prepared for what lies ahead and not pay attention to what is different, such as an atypical location for a runway hold position marking
  • When it comes to hand and arm signals, variations may exist
    • If any questions come up while taxiing, stop, and try to get clarification before proceeding
  • When taxiing and determining wind direction, make sure you account for the resultant wind
  • Consider the use of heading bugs to remember where the wind is coming from
  • While it is best practice to always apply taxi corrections, regardless of wind velocity, it is imperative these corrections be used any time you can feel even the slightest movement in the yoke
  • While it is best practice to always apply taxi corrections, regardless of wind velocity, it is imperative these corrections be used any time you can feel even the slightest movement in the yoke
  • During ground operations, jet blast, prop wash, and rotor wash (types of thrust stream turbulence) can cause damage and upsets if encountered at close range
    • Pilots should consider the effects of jet blast, prop wash, and rotor wash on aircraft, vehicles, and maintenance equipment during ground operations
  • Additional resources are available through tools such as the FAA's Runway Safety Simulator
  • Remember when parking, to park in such a way to avoid inevitable jet blast (especially from larger aircraft), use tiedowns, and install control locks or covers as appropriate
  • Don't be afraid to practice if you need it
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References: