FAA Part 107 Remote Pilot (UAG) flashcards
218 free flashcards. Tap a card to flip it.
National Security Area (NSA)
Flip cardAirspace established over sensitive locations (e.g., dams, power plants) where pilots are requested to voluntarily avoid flight; can become mandatory via NOTAM.
- Voluntary avoidance requested normally
- NOTAM can make restriction mandatory
- Charted with a dashed magenta outline and 'NSA' label
Memory trick: NSA = 'Nicely Stay Away' unless a NOTAM says you must.
TAF FM Group
Flip cardIn a Terminal Aerodrome Forecast, 'FM' followed by a time indicates a rapid, significant, and lasting change in conditions beginning at that time, replacing all prior forecast conditions.
- FM time is given in four digits UTC (e.g., FM1800 = 1800Z)
- Conditions after FM remain valid until the next FM or BECMG group
- Differs from TEMPO, which denotes temporary, short-lived fluctuations
Memory trick: 'FM = From this moment forward — like flipping a light switch instantly.'
LAANC (Low Altitude Authorization and Notification Capability)
Flip cardAn automated system that provides near real-time airspace authorization for Part 107 operations in controlled airspace up to pre-set altitudes on UAS Facility Maps.
- Automated, near-instant approval
- Uses UAS Facility Maps for grid-based max altitudes
- Alternative to manual DroneZone request
- Higher altitudes above facility map still need a waiver or further coordination
Memory trick: 'LAANC = Lightning-fast Approval Automated Near Control towers.'
External Load Operations
Flip cardOperations in which a sUAS carries a load attached externally (e.g., via sling); the load must be secured to prevent shifting or excessive pendulum motion that could destabilize the aircraft's center of gravity.
- External loads must not adversely affect flight characteristics
- Improper securing causes pendulum oscillation
- CG shifts dynamically with a swinging load
- 107.19 addresses securing objects carried or dropped
Memory trick: A swinging load is a wrecking ball to your CG
Temporary Flight Restrictions (TFRs)
Flip cardTFRs are published via NOTAM to restrict flight in a defined area, commonly for wildfires, VIP movements, or major events.
- Published as NOTAMs and must be checked before flight
- Wildfire TFRs protect firefighting aircraft operations
- Flying in an active TFR without authorization is a violation
Memory trick: 'Fire means check the wire' — check NOTAMs before flying near wildfires.
Washington D.C. FRZ / P-56
Flip cardA highly restricted airspace area around Washington, D.C. including prohibited area P-56, where sUAS operations are generally banned without specific FAA/TSA security authorization.
- Includes National Mall, White House, Capitol area
- Standard LAANC does not apply
- Requires special security-related authorization
- One of the most heavily enforced restricted zones in the US
Memory trick: D.C. = 'Don't fly, Complicated clearance needed'.
Class A Airspace
Flip cardAirspace extending from 18,000 feet MSL up to and including FL600, used for IFR operations; not depicted with boundaries on sectional charts.
- Begins at 18,000 ft MSL
- All operations require an IFR clearance
- Part 107 UAS operations cannot practically reach this altitude
- No LAANC authorization exists for Class A
Memory trick: 'A is for Altitude sky-high' — 18,000 feet and above.
Physical/Mental Condition (107.17)
Flip cardProhibits a person from acting as RPIC or manipulating sUAS controls while they know or have reason to know of a condition that would interfere with safe operation.
- No FAA medical certificate required for Part 107
- Applies to illness, medication, or fatigue
- Mirrors the manned-aircraft standard in 61.53
Memory trick: 'Groggy pilot, grounded drone.'
LAANC Authorization Limits
Flip cardLAANC provides near real-time airspace authorization for controlled airspace operations but does not separate the sUAS from other traffic; the remote PIC remains fully responsible for collision avoidance.
- LAANC grants access, not traffic separation
- Remote PIC must continuously see and avoid manned aircraft
- Authorization can be for a fixed altitude ceiling by grid
- Pilot must yield right of way to manned aircraft
Memory trick: LAANC opens the door, it doesn't watch your back
Class E Airspace Default Floor
Flip cardIn areas without a specifically designated lower floor, Class E airspace over the contiguous U.S. begins at 14,500 feet MSL and extends up to 18,000 feet MSL.
- Default floor: 14,500 ft MSL
- Designated floors near airports can be 700 ft or 1,200 ft AGL
- Class E ends at 18,000 ft MSL, the base of Class A
- Rarely relevant to Part 107 UAS operations due to the 400 ft AGL ceiling
Memory trick: '14.5 is the default ceiling of the sky's basement' when nothing else is marked.
Certificate of Waiver (107.200)
Flip cardA waiver granted by the FAA that allows a sUAS operation to deviate from certain Part 107 provisions if the applicant demonstrates the operation can be conducted safely.
- Required for BVLOS, night ops without proper waiver categories, or other rule deviations
- Applicant must show equivalent level of safety
- Submitted through FAA DroneZone
Memory trick: 'Waive the rule, prove it's cool (safe).'
Accident Reporting (107.9)
Flip cardRemote pilots must report to the FAA within 10 calendar days if an operation causes serious injury, loss of consciousness, or property damage of $500 or more.
- Threshold: $500 property damage or serious injury
- 10 calendar day reporting window
- Report submitted to FAA, not NTSB
Memory trick: 'Five hundred bucks, ten days, tell the FAA, always.'
GPS Signal Loss Response
Flip cardWhen GPS is lost, sUAS often revert to attitude-hold mode without position hold; the PIC must take manual control since GPS-dependent functions like RTH become unreliable.
- Attitude-hold mode requires manual pilot input to control drift
- RTH/failsafe functions typically depend on GPS
- PIC in-flight emergency authority under 107.21 allows deviation as needed
Memory trick: No GPS, no autopilot — grab the sticks yourself.
Class D Airspace
Flip cardControlled airspace around airports with an operating control tower, typically extending from the surface to 2,500 feet AGL.
- Requires ATC authorization for Part 107 operations
- Depicted with a dashed blue line on sectionals
- Reverts to Class E or G when tower is not in operation
- LAANC may be available for many Class D facilities
Memory trick: Dashed Blue Circle = 'Dial-in with ATC before you fly'
Preflight Assessment (107.49)
Flip cardThe set of operating-environment and equipment checks a remote PIC must complete before every UAS flight under Part 107.
- Must assess local weather
- Must assess local airspace/flight restrictions
- Must assess persons/property on surface
- Must check control link and aircraft condition
Memory trick: WASP: Weather, Airspace, Surface hazards, People/property
Remote Pilot Currency Requirement
Flip cardPart 107 remote pilots must pass a recurrent knowledge test or complete recurrent online training every 24 calendar months to remain current.
- Recurrent test/training required every 24 calendar months
- No flight review or logged flight hours required
- Certificate itself does not expire
Memory trick: '24 months, test again' keeps your remote pilot privileges legal.
Sea Breeze
Flip cardA local wind that blows from the sea toward the land during the day, caused by land heating faster than water and creating a pressure difference that draws cooler ocean air onshore.
- Occurs during daytime, typically strongest in the afternoon
- Reverses at night as a land breeze once land cools faster than water
- Can create localized turbulence or wind shifts along coastlines
Memory trick: 'Sea breeze = Sun heats Sand fast, cooler Sea air Surges in by day.'
Maximum Takeoff Weight (Part 107)
Flip cardPart 107 sUAS, including everything on board or attached, must weigh less than 55 lbs at takeoff unless operating under an exemption.
- 55 lb limit includes payload and any external attachments
- Total weight = empty weight + payload + accessory weight
- Exceeding manufacturer's structural limit is also unsafe even if under 55 lb
- Weight and balance affects flight characteristics and control
Memory trick: 55 is the ceiling — add it all before you fly
Ceiling (METAR)
Flip cardThe height above ground of the lowest cloud layer reported as broken or overcast, or the vertical visibility into an indefinite ceiling.
- FEW and SCT layers never count as a ceiling
- BKN and OVC layers define a ceiling
- The LOWEST BKN/OVC layer sets the ceiling height
- Vertical visibility (VV) is used when the sky is obscured
Memory trick: 'Ceiling starts at Broken' — FEW and SCT don't block the sky enough to count.
Aviation Weather Briefing Sources
Flip cardOfficial sources such as 1-800-WX-BRIEF or FAA-recognized apps provide aviation weather, NOTAMs, and TFR information necessary for safe flight planning.
- 1-800-WX-BRIEF is the traditional Flight Service briefing line
- Briefings include NOTAMs, TFRs, and weather forecasts
- Non-aviation weather apps often lack critical flight data
Memory trick: 'WX-BRIEF before you lift!' — always call or check official sources first.
Civil Twilight Lighting Requirement
Flip cardsUAS operations during civil twilight require anti-collision lighting visible for at least 3 statute miles.
- Civil twilight: 30 min before sunrise and 30 min after sunset
- Anti-collision light must have a flash rate sufficient to avoid collision hazard
- Daylight-only rule was amended to permit twilight ops with lighting
Memory trick: 'Twilight needs a light seen for 3' — 3 statute miles visibility.
Controlled Airspace Authorization
Flip cardPart 107 requires remote pilots to obtain ATC authorization before operating in Class B, C, D, or surface Class E airspace, typically via LAANC.
- LAANC provides near-real-time authorization for many airports
- DroneZone can be used when LAANC is unavailable
- Class G airspace requires no ATC authorization
Memory trick: B-C-D-E(surface) need a permission slip; G is free to fly.
NOTAM Review
Flip cardPreflight requirement to check Notices to Air Missions for time-critical aeronautical information affecting the operating area.
- Required under 14 CFR 107.49 preflight familiarization
- Covers TFRs, obstacle lighting outages, runway closures, and more
- Available through FAA NOTAM search, Flight Service, or apps
- Complements but does not replace airspace authorization
Memory trick: NOTAM = 'Notice Of Trouble Ahead, Mission-critical'
Remote Pilot Certificate Eligibility
Flip cardThe basic requirements a person must meet under 14 CFR 107.61 to be issued a Remote Pilot Certificate with a small UAS rating.
- Must be at least 16 years old
- Must read, speak, write, and understand English
- Must be in a physical/mental condition to safely operate a sUAS
- Must pass the initial aeronautical knowledge test
Memory trick: 'ALEK' — Age, Language, English self-fitness, Knowledge test
sUAS Maintenance Responsibility
Flip cardUnder Part 107, the remote pilot in command is responsible for ensuring the aircraft is in a condition for safe operation, generally by following manufacturer maintenance and inspection guidance rather than a certificated mechanic requirement.
- No FAA-mandated inspection program for most sUAS
- Remote PIC bears ultimate responsibility
- Manufacturer's guidance is the typical maintenance reference
- Recordkeeping is good practice though not always required by rule
Memory trick: No mechanic needed — the PIC is the guardian of airworthiness
Altitude Exception Near Structures (107.51(b)(2))
Flip cardAn sUAS may fly higher than 400 feet AGL if it remains within 400 horizontal feet of a structure and does not exceed 400 feet above the structure's immediate uppermost limit.
- Applies within 400 horizontal feet of a structure
- Allows altitude up to structure height + 400 feet
- No waiver required for this built-in exception
- Still must comply with other airspace restrictions
Memory trick: 'Tower plus 400' — the sky's the limit near tall structures.
Manual Airspace Authorization
Flip cardWhen LAANC automated authorization isn't available for a location/altitude, pilots must file a manual request via FAADroneZone, which can take up to 90 days to process.
- Manual requests are submitted through FAADroneZone
- Processing may take up to 90 days
- LAANC is the faster, automated alternative when available
Memory trick: 'No LAANC? Plan for 90 days with DroneZone.'
Class E Surface Area Symbol
Flip cardA fading magenta vignette on a sectional chart depicts Class E airspace extending to the surface, commonly found at airports with instrument approaches but no continuous tower operation.
- Fading magenta shading = Class E to surface
- Different from solid magenta (Class E floor 700 ft AGL)
- Different from dashed blue line (Class D towered airport)
Memory trick: Fading magenta = Class E fading down to the ground.
Certificate of Waiver
Flip cardAn FAA-issued authorization under 107.200 permitting deviation from specific Part 107 provisions when the operation can be conducted safely.
- Applied for via FAA DroneZone
- Common waivers: BVLOS, night ops (largely superseded by rule changes), operations over people
- Must demonstrate equivalent level of safety
Memory trick: 'Need an exception? Get a waiver, not a NOTAM.'
Class C Airspace
Flip cardControlled airspace around medium-sized airports with an operating control tower and radar approach control, depicted as two concentric circles.
- Typically has a 5 NM inner core surface to 4,000 ft AGL and a 10 NM shelf
- Requires ATC authorization under Part 107.41
- Depicted with solid magenta circles on sectional charts
- Provides radar services to arriving/departing traffic
Memory trick: Class C = 'Circles, Circles' - two rings around the airport
Part 107 Weather Minimums
Flip card14 CFR 107.51 sets minimum visibility and cloud clearance requirements for small UAS operations.
- Minimum visibility: 3 statute miles from control station
- Cloud clearance: 500 ft below, 2000 ft horizontal
- Max altitude 400 ft AGL, max groundspeed 87 knots (100 mph)
Memory trick: 'See three, clear the clouds' — 3SM visibility, 500 below/2000 around clouds.
UAS Facility Maps
Flip cardCharts showing the maximum altitude the FAA will automatically authorize sUAS operations via LAANC in specific grid areas of controlled airspace.
- Grid values are ceilings, not floors
- Requests above the grid value require manual FAA review
- Values vary by location based on manned aircraft traffic patterns
Memory trick: Grid number = the ceiling LAANC lets you fly under instantly.
Cold Front Passage
Flip cardA cold front occurs when a cold air mass advances and undercuts a warmer air mass, producing a narrow band of intense weather followed by clearing.
- Wind shifts direction (often SW to NW) at passage
- Temperature drops and pressure rises after passage
- Narrow band of showers/thunderstorms occurs at the front itself
Memory trick: 'Cold front clears the air' — storms pass, then skies clear and cool.
Crosswind Component Calculation
Flip cardThe crosswind component is the portion of wind blowing perpendicular to the runway/launch heading, calculated as wind speed × sine of the angle between wind direction and heading.
- Crosswind component = wind speed × sin(angle difference)
- Compare to the manufacturer's maximum demonstrated crosswind component
- Headwind component = wind speed × cos(angle difference)
Memory trick: Sine for shove sideways, cosine for coming at you head-on.
Orographic Lifting / Mountain Wave
Flip cardForced ascent of air over rising terrain, which can create mountain waves and severe rotor turbulence on the lee side.
- Windward side: forced ascent, cloud formation, precipitation
- Lee side: descending air, mountain waves, rotor turbulence
- Turbulence can extend far downwind and be severe
- Rotor clouds may form beneath the wave crest
Memory trick: 'Lee side leaps and rolls' — air rolls into rotors after crossing the ridge.
Wildlife Refuges and UAS Operations
Flip cardAreas where the FAA has no specific airspace restriction, but the U.S. Fish and Wildlife Service and refuge managers may impose land-use or wildlife-disturbance rules affecting UAS.
- No dedicated FAA airspace classification for refuges
- FWS voluntary guidance suggests avoiding low-altitude disturbance of wildlife
- Individual refuges may require separate special use permits for drones
- Distinct from FAA-controlled airspace authorization requirements
Memory trick: Refuge = 'Respect the Refuge' even without FAA rule
Class G Airspace Authorization
Flip cardClass G is uncontrolled airspace where Part 107 sUAS operations require no ATC authorization, subject to standard Part 107 operating rules.
- Uncontrolled airspace, no ATC authorization needed
- Standard altitude and visibility rules still apply
- Controlled airspace (B, C, D, surface E) requires authorization under 107.41
Memory trick: 'Green light in Class G — go without asking'
Mechanical Turbulence
Flip cardTurbulence caused by wind flow being disrupted as it passes over or around surface obstructions like buildings, trees, or terrain.
- Strongest immediately downwind of the obstruction
- Increases with wind speed and obstruction height
- Can create rotors and sudden altitude/attitude changes for sUAS
Memory trick: 'Mechanical = Machines and buildings mechanically chop the wind into eddies.'
Freezing Level
Flip cardThe altitude at which the outside air temperature reaches 0°C, calculated using surface temperature and the standard lapse rate, important for assessing structural icing risk.
- Standard lapse rate is 2°C per 1,000 feet
- Freezing level altitude = surface temp (°C) ÷ 2 × 1,000 feet
- Actual freezing level can vary due to inversions or moisture, so pilot reports and forecasts should be cross-checked
Memory trick: 'Divide by two, multiply by a thousand — count down degrees like steps up a ladder to the freezing floor.'
Maximum Altitude (Part 107.51)
Flip cardSmall UAS operations are generally limited to 400 feet above ground level unless flying near a taller structure or holding a waiver.
- 400 ft AGL is the default ceiling
- Exception exists within 400 ft laterally of a structure
- Waivers can authorize higher altitudes
Memory trick: '400 is the fence' — Part 107 caps altitude at 400 feet.
Thunderstorm Mature Stage
Flip cardThe most hazardous phase of a thunderstorm's life cycle, featuring simultaneous updrafts and downdrafts, heavy rain, lightning, hail, and gusty surface winds.
- Begins when precipitation starts falling and reaches the surface
- Downdrafts spread out at the surface as gust fronts
- Most severe turbulence, wind shear, and icing occur during this stage
Memory trick: 'Mature = MAX mayhem — up and down drafts duking it out.'
Density Altitude
Flip cardPressure altitude corrected for nonstandard temperature; represents the altitude the aircraft 'feels' it is flying at aerodynamically.
- Rule of thumb: DA ≈ pressure altitude + (120 × temp deviation from standard)
- Higher DA = thinner air = reduced lift, thrust, and climb performance
- Hot, high, and humid conditions increase density altitude
Memory trick: 'High, hot, humid' all push density altitude up and performance down.
UAS Registration Threshold
Flip cardUAS weighing more than 0.55 lbs (250g) up to 55 lbs must be registered with the FAA regardless of purpose of flight.
- Threshold: 0.55 lbs to 55 lbs
- Applies to recreational and commercial drones
- Registration must occur before first flight
Memory trick: 'Over half a pound, register now.'
Weight vs. Endurance Tradeoff
Flip cardIncreasing payload weight on an sUAS requires more thrust and battery current, directly reducing available flight time.
- More weight = more thrust needed = more current draw
- Endurance and payload capacity are inversely related
- Pilots must balance mission payload needs against acceptable flight time
Memory trick: Heavier load, hungrier motors, shorter flight.
Aft CG Effects
Flip cardA center of gravity aft of the approved limit reduces longitudinal stability and increases the risk of an uncommanded pitch-up and stall.
- Reduces stick force gradient/stability
- Can cause uncontrollable pitch-up
- Lowers stall speed slightly but raises loss-of-control risk
Memory trick: Tail-heavy plane rears back like a startled horse.
Preflight Inspection (107.49)
Flip cardBefore flight, the RPIC must assess the operating environment and inspect the sUAS to ensure it is safe to operate.
- Check local weather and airspace conditions
- Check for hazards to persons/property on the surface
- Verify control links, communication systems, and battery charge are adequate
Memory trick: Think WEATHER-LINK-BATTERY before every launch.
Right of Way Rule (107.37)
Flip cardRemote pilots must always yield the right of way to manned aircraft and maneuver to avoid collisions.
- sUAS always yields to manned aircraft
- Applies in all airspace classes
- Remote pilot must see and avoid other aircraft
Memory trick: 'Manned always wins, drones give in.'
Part 107 Duty/Rest Requirements
Flip cardPart 107 does not impose specific duty-time or rest-period limits like Parts 117 or 135; instead, remote pilots must self-certify their fitness for duty under 107.27.
- No prescribed duty/rest hour limits in Part 107
- 107.27 prohibits operating while unfit due to fatigue, alcohol, or drugs
- Fatigue management is the pilot's personal responsibility
- Contrasts with Part 117 crew rest rules for manned commercial flights
Memory trick: No clock rules here—just self-check with IMSAFE before every flight.
Disaster/Hazard TFR (91.137)
Flip cardA Temporary Flight Restriction established to protect persons and property during disaster relief operations, applicable to all aircraft including sUAS, requiring specific authorization for entry.
- Applies to manned and unmanned aircraft alike
- Entry requires authorization from the FAA or responsible agency
- Prevents interference with firefighting, search and rescue, or law enforcement
Memory trick: Disaster zones aren't drone zones unless you're cleared in.
Small UAS Weight Definition
Flip cardA small unmanned aircraft under Part 107 is one weighing less than 55 pounds at takeoff, including everything on board or attached.
- Includes payload, batteries, and attachments
- Aircraft ≥55 lbs require different certification
- Weight is the basis for Part 107 applicability
Memory trick: 'Fifty-Five to Fly Free' under Part 107
Precipitation Effects on sUAS Performance
Flip cardMoisture from rain can add airframe weight and compromise electrical component reliability, degrading motor performance and battery efficiency even in aircraft rated for light precipitation.
- Moisture adds weight, increasing power demand
- Water intrusion risks corrosion or short circuits in electronics
- Manufacturer precipitation ratings do not eliminate all performance risk
Memory trick: Rain doesn't just get you wet — it weighs you down and shorts out your circuits.
Wind Effects on Battery Endurance
Flip cardHeadwinds reduce groundspeed, increasing flight time and battery consumption needed to reach a destination, which can shorten usable mission range.
- Headwind reduces groundspeed, increases battery use
- Tailwind increases groundspeed, saves battery
- Crosswinds require heading correction
Memory trick: Fighting a headwind drains your battery like running against a treadmill.
DC Special Flight Rules Area (SFRA)
Flip cardA highly restricted airspace surrounding Washington, D.C. where sUAS operations are generally prohibited without specific security-based authorization from the FAA and TSA.
- Includes an inner Flight Restricted Zone (FRZ) with even tighter rules
- LAANC does not apply within this airspace
- Violations can result in severe civil and criminal penalties
Memory trick: 'DC = Definitely Closed' to casual drone flights
Night Operations Lighting (107.29)
Flip cardRequirement for anti-collision lighting on sUAS conducting operations during civil twilight or night, allowing other aircraft to see and avoid the drone.
- Anti-collision light visible for 3 statute miles
- Flash rate must be sufficient to avoid collision hazard
- Applies from official sunset to sunrise (per current rule, civil twilight windows included)
- Remote PIC must complete recurrent training covering night operations
Memory trick: 3 miles, flash, avoid the crash
Class E Surface Area
Flip cardControlled airspace extending to the surface around certain airports, depicted by a dashed magenta line on sectional charts; requires authorization for sUAS operations like Class D.
- Dashed magenta line = Class E to surface
- Common at non-towered airports with instrument approaches
- Requires LAANC or manual authorization to operate
Memory trick: Dashed magenta = 'Down to the ground' controlled airspace.
Standard Lapse Rate
Flip cardIn the standard atmosphere, temperature decreases at a rate of approximately 2°C (3.5°F) per 1,000 feet of altitude gain.
- Standard sea-level temperature is 15°C (59°F)
- Standard sea-level pressure is 29.92 inHg
- Used to estimate temperature and density altitude changes with altitude
Memory trick: 'Two degrees, every thousand feet — like a countdown clock cooling the sky.'
Sectional Chart Airspace Boundary Colors
Flip cardDashed blue lines denote Class D airspace (towered airports); dashed magenta lines denote Class E surface areas (typically non-towered or part-time towered airports).
- Blue dashed circle = Class D, control tower in operation
- Magenta dashed circle = Class E surface area extending to ground
- Solid magenta line = Class E starting at 700 ft AGL
- Solid blue line = Class B; solid magenta band circles = Class C
Memory trick: Blue Dash = Big Tower (D); Magenta Dash = Missing Tower (E surface)
PIREP
Flip cardA Pilot Report describing actual weather conditions encountered in flight, such as turbulence, icing, or cloud tops.
- Submitted voluntarily by pilots in flight
- Provides real-time confirmation of forecast accuracy
- Used to update or issue AIRMETs/SIGMETs
- Coded format includes location, time, altitude, aircraft type, and conditions
Memory trick: 'PIREP = Pilot Personally Reports' actual conditions, not a forecast.
Falsification of Records (107.13)
Flip cardProhibits knowingly making fraudulent or intentionally false entries in any record or report required under Part 107.
- Applies to maintenance logs, flight records, and reports
- Violation can lead to certificate suspension or revocation
- Separate from accident reporting requirements under 107.9
Memory trick: Fake logs, real consequences — 107.13 catches liars.
LiPo Battery Swelling Hazard
Flip cardSwelling indicates internal cell damage or gas buildup in a lithium polymer battery, creating fire/explosion risk; such batteries must be removed from service.
- Never charge, fly, or puncture a swollen LiPo
- Store and dispose of damaged batteries per hazmat guidance
- Inspect batteries for swelling, punctures, and damage every preflight
Memory trick: 'Puffy pack, pull it back' — retire swollen batteries.