NTSB investigations, OK
769 cases where the phase of flight was Landing.
Cases per year
| 1964 | 36 |
|---|---|
| 1965 | 39 |
| 1966 | 42 |
| 1967 | 56 |
| 1968 | 42 |
| 1969 | 34 |
| 1970 | 26 |
| 1971 | 28 |
| 1972 | 21 |
| 1973 | 19 |
| 1974 | 20 |
| 1975 | 17 |
| 1976 | 11 |
| 1977 | 17 |
| 1978 | 15 |
| 1979 | 9 |
| 1980 | 13 |
| 1981 | 34 |
| 1982 | 22 |
| 1983 | 12 |
| 1984 | 19 |
| 1985 | 10 |
| 1986 | 4 |
| 1987 | 12 |
| 1988 | 4 |
| 1989 | 6 |
| 1990 | 2 |
| 1991 | 5 |
| 1992 | 5 |
| 1993 | 3 |
| 1994 | 5 |
| 1995 | 8 |
| 1996 | 7 |
| 1997 | 6 |
| 1998 | 9 |
| 1999 | 9 |
| 2000 | 5 |
| 2001 | 4 |
| 2002 | 3 |
| 2003 | 5 |
| 2004 | 6 |
| 2005 | 8 |
| 2006 | 2 |
| 2007 | 12 |
| 2008 | 4 |
| 2009 | 4 |
| 2010 | 7 |
| 2011 | 7 |
| 2012 | 3 |
| 2013 | 2 |
| 2014 | 1 |
| 2015 | 3 |
| 2016 | 9 |
| 2017 | 5 |
| 2018 | 2 |
| 2019 | 8 |
| 2020 | 4 |
| 2021 | 3 |
| 2022 | 5 |
| 2023 | 9 |
| 2024 | 8 |
| 2025 | 10 |
| 2026 | 3 |
Where
Latest cases
Query with SQL
duckdb -csv -c "WITH phase_names(main, name) AS (VALUES (100, 'Prior to flight'), (150, 'Standing'), (200, 'Pushback/towing'), (250, 'Taxi'), (300, 'Takeoff'), (350, 'Initial climb'), (400, 'Enroute'), (450, 'Maneuvering'), (500, 'Approach'), (550, 'Landing'), (600, 'Emergency descent'), (650, 'Uncontrolled descent'), (700, 'Post-impact'), (750, 'After landing'), (800, 'Other'), (990, 'Unknown')),
crosswalk(code, main, name) AS (VALUES (500, 150, 'Standing'), (501, 150, 'Standing - pre-flight'), (502, 150, 'Standing - starting engine(s)'), (503, 150, 'Standing - engine(s) operating'), (504, 150, 'Standing - engine(s) not operating'), (505, 150, 'Standing - idling rotors'), (510, 250, 'Taxi'), (511, 200, 'Taxi - pushback/tow'), (512, 250, 'Taxi - to takeoff'), (513, 250, 'Taxi - from landing'), (514, 250, 'Taxi - aerial'), (520, 300, 'Takeoff'), (521, 300, 'Takeoff - roll/run'), (522, 350, 'Takeoff - initial climb'), (523, 300, 'Takeoff - aborted'), (530, 400, 'Climb'), (531, 400, 'Climb - to cruise'), (540, 400, 'Cruise'), (541, 400, 'Cruise - normal'), (542, 400, 'Maneuvering - holding (IFR)'), (550, 400, 'Descent'), (551, 400, 'Descent - normal'), (552, 600, 'Descent - emergency'), (553, 650, 'Descent - uncontrolled'), (560, 500, 'Approach'), (561, 500, 'Approach - VFR pattern - downwind'), (562, 500, 'Approach - VFR pattern - base turn'), (563, 500, 'Approach - VFR pattern - base leg/base to final'), (564, 500, 'Approach - VFR pattern - final approach'), (565, 500, 'Go-around (VFR)'), (566, 500, 'Approach - IAF to FAF/outer marker (IFR)'), (567, 500, 'Approach - FAF/outer marker to threshold (IFR)'), (568, 500, 'Circling (IFR)'), (569, 500, 'Missed approach (IFR)'), (570, 550, 'Landing'), (571, 550, 'Landing - flare/touchdown'), (572, 550, 'Landing - roll'), (573, 550, 'Landing - aborted'), (574, 550, 'Emergency landing'), (575, 550, 'Emergency landing after takeoff'), (576, 600, 'Emergency descent/landing'), (580, 450, 'Maneuvering'), (581, 450, 'Maneuvering - aerial application'), (582, 450, 'Maneuvering - turn to reverse direction'), (583, 450, 'Maneuvering - turn to landing area (emergency)'), (590, 450, 'Hover'), (591, 450, 'Hover - in ground effect'), (592, 450, 'Hover - out of ground effect'), (600, 800, 'Other'), (610, 990, 'Unknown')),
current_codes AS (
SELECT e.case_mkey, TRY_CAST(e.\"tier1Number\" AS INTEGER) AS code,
row_number() OVER (PARTITION BY e.case_mkey ORDER BY coalesce(e.\"isDefiningEvent\", false) DESC, e.position) AS n
FROM 'https://openairdocs.org/data/latest/ntsb_events.parquet' e
WHERE e.aircrafts_position = 1 AND e.\"tier1Number\" GLOB '[1-9][0-9]*'
AND (e.\"isDefiningEvent\" OR e.case_mkey IN (SELECT \"mKey\" FROM 'https://openairdocs.org/data/latest/ntsb_case_detail.parquet' WHERE \"isPre1982\"))
),
phases AS (
SELECT case_mkey, 'current' AS scheme, code, CASE WHEN code >= 990 THEN 990 ELSE code // 50 * 50 END AS main
FROM current_codes WHERE n = 1
UNION ALL
SELECT o.case_mkey, 'older', o.\"phaseOfFlightCode\", w.main
FROM 'https://openairdocs.org/data/latest/ntsb_occurrences.parquet' o JOIN crosswalk w ON w.code = o.\"phaseOfFlightCode\"
WHERE o.aircrafts_position = 1 AND o.\"occurrenceNumber\" = 1 AND o.case_mkey NOT IN (SELECT case_mkey FROM current_codes)
),
case_phases AS (
SELECT p.*, c.\"eventDate\", c.\"highestInjuryLevel\" = 'Fatal' AS fatal, a.aircraft_model_code
FROM phases p JOIN 'https://openairdocs.org/data/latest/ntsb_case_detail.parquet' c ON c.\"mKey\" = p.case_mkey
LEFT JOIN 'https://openairdocs.org/data/latest/ntsb_aircrafts.parquet' a ON a.case_mkey = p.case_mkey AND a.position = 1
WHERE c.\"eventDate\" >= DATE '1962-01-01' AND p.main IN (SELECT main FROM phase_names)
)
SELECT c.\"ntsbNumber\", c.\"eventDate\", c.\"eventType\", c.\"eventCity\", c.\"eventStateOrRegion\", a.n_number, a.\"aircraftMake\", a.\"aircraftModel\", c.\"highestInjuryLevel\", c.\"totalFatal\", c.\"completionStatus\", c.report_url
FROM 'https://openairdocs.org/data/latest/ntsb_case_detail.parquet' c LEFT JOIN 'https://openairdocs.org/data/latest/ntsb_aircrafts.parquet' a ON a.case_mkey = c.\"mKey\" AND a.position = 1
WHERE c.\"eventStateOrRegion\" = 'OK' AND c.\"eventCountry\" = 'USA'
AND c.\"mKey\" IN (SELECT case_mkey FROM case_phases WHERE main = 550)
ORDER BY c.\"eventDate\" DESC, c.\"ntsbNumber\" DESC"Prints the whole list as CSV. It reads the release’s Parquet files over HTTPS, so there’s nothing to download first. Install DuckDB to run it.
WITH phase_names(main, name) AS (VALUES (100, 'Prior to flight'), (150, 'Standing'), (200, 'Pushback/towing'), (250, 'Taxi'), (300, 'Takeoff'), (350, 'Initial climb'), (400, 'Enroute'), (450, 'Maneuvering'), (500, 'Approach'), (550, 'Landing'), (600, 'Emergency descent'), (650, 'Uncontrolled descent'), (700, 'Post-impact'), (750, 'After landing'), (800, 'Other'), (990, 'Unknown')),
crosswalk(code, main, name) AS (VALUES (500, 150, 'Standing'), (501, 150, 'Standing - pre-flight'), (502, 150, 'Standing - starting engine(s)'), (503, 150, 'Standing - engine(s) operating'), (504, 150, 'Standing - engine(s) not operating'), (505, 150, 'Standing - idling rotors'), (510, 250, 'Taxi'), (511, 200, 'Taxi - pushback/tow'), (512, 250, 'Taxi - to takeoff'), (513, 250, 'Taxi - from landing'), (514, 250, 'Taxi - aerial'), (520, 300, 'Takeoff'), (521, 300, 'Takeoff - roll/run'), (522, 350, 'Takeoff - initial climb'), (523, 300, 'Takeoff - aborted'), (530, 400, 'Climb'), (531, 400, 'Climb - to cruise'), (540, 400, 'Cruise'), (541, 400, 'Cruise - normal'), (542, 400, 'Maneuvering - holding (IFR)'), (550, 400, 'Descent'), (551, 400, 'Descent - normal'), (552, 600, 'Descent - emergency'), (553, 650, 'Descent - uncontrolled'), (560, 500, 'Approach'), (561, 500, 'Approach - VFR pattern - downwind'), (562, 500, 'Approach - VFR pattern - base turn'), (563, 500, 'Approach - VFR pattern - base leg/base to final'), (564, 500, 'Approach - VFR pattern - final approach'), (565, 500, 'Go-around (VFR)'), (566, 500, 'Approach - IAF to FAF/outer marker (IFR)'), (567, 500, 'Approach - FAF/outer marker to threshold (IFR)'), (568, 500, 'Circling (IFR)'), (569, 500, 'Missed approach (IFR)'), (570, 550, 'Landing'), (571, 550, 'Landing - flare/touchdown'), (572, 550, 'Landing - roll'), (573, 550, 'Landing - aborted'), (574, 550, 'Emergency landing'), (575, 550, 'Emergency landing after takeoff'), (576, 600, 'Emergency descent/landing'), (580, 450, 'Maneuvering'), (581, 450, 'Maneuvering - aerial application'), (582, 450, 'Maneuvering - turn to reverse direction'), (583, 450, 'Maneuvering - turn to landing area (emergency)'), (590, 450, 'Hover'), (591, 450, 'Hover - in ground effect'), (592, 450, 'Hover - out of ground effect'), (600, 800, 'Other'), (610, 990, 'Unknown')),
current_codes AS (
SELECT e.case_mkey, TRY_CAST(e."tier1Number" AS INTEGER) AS code,
row_number() OVER (PARTITION BY e.case_mkey ORDER BY coalesce(e."isDefiningEvent", false) DESC, e.position) AS n
FROM 'https://openairdocs.org/data/latest/ntsb_events.parquet' e
WHERE e.aircrafts_position = 1 AND e."tier1Number" GLOB '[1-9][0-9]*'
AND (e."isDefiningEvent" OR e.case_mkey IN (SELECT "mKey" FROM 'https://openairdocs.org/data/latest/ntsb_case_detail.parquet' WHERE "isPre1982"))
),
phases AS (
SELECT case_mkey, 'current' AS scheme, code, CASE WHEN code >= 990 THEN 990 ELSE code // 50 * 50 END AS main
FROM current_codes WHERE n = 1
UNION ALL
SELECT o.case_mkey, 'older', o."phaseOfFlightCode", w.main
FROM 'https://openairdocs.org/data/latest/ntsb_occurrences.parquet' o JOIN crosswalk w ON w.code = o."phaseOfFlightCode"
WHERE o.aircrafts_position = 1 AND o."occurrenceNumber" = 1 AND o.case_mkey NOT IN (SELECT case_mkey FROM current_codes)
),
case_phases AS (
SELECT p.*, c."eventDate", c."highestInjuryLevel" = 'Fatal' AS fatal, a.aircraft_model_code
FROM phases p JOIN 'https://openairdocs.org/data/latest/ntsb_case_detail.parquet' c ON c."mKey" = p.case_mkey
LEFT JOIN 'https://openairdocs.org/data/latest/ntsb_aircrafts.parquet' a ON a.case_mkey = p.case_mkey AND a.position = 1
WHERE c."eventDate" >= DATE '1962-01-01' AND p.main IN (SELECT main FROM phase_names)
)
SELECT c."ntsbNumber", c."eventDate", c."eventType", c."eventCity", c."eventStateOrRegion", a.n_number, a."aircraftMake", a."aircraftModel", c."highestInjuryLevel", c."totalFatal", c."completionStatus", c.report_url
FROM 'https://openairdocs.org/data/latest/ntsb_case_detail.parquet' c LEFT JOIN 'https://openairdocs.org/data/latest/ntsb_aircrafts.parquet' a ON a.case_mkey = c."mKey" AND a.position = 1
WHERE c."eventStateOrRegion" = 'OK' AND c."eventCountry" = 'USA'
AND c."mKey" IN (SELECT case_mkey FROM case_phases WHERE main = 550)
ORDER BY c."eventDate" DESC, c."ntsbNumber" DESCRun it at the DuckDB prompt, or in any tool that reads Parquet over HTTPS. More ways to query the release are on Use the data.
NTSB CEN26LA206Accident · No injuriesClass 4 · LimitedFinal reportPitts Special S-1S · Bartlesville, OKThe pilot’s failure to maintain control during the landing rollout and subsequent aborted landing.NTSB CEN26LA170Accident · Minor injuriesClass 4 · LimitedFinal reportPiper PA 31P 350 · Ardmore, OKThe pilot’s failure to maintain control of the airplane while landing on a wet runway with a tailwind.NTSB CEN26LA160Accident · No injuriesClass 4 · LimitedFinal reportCessna 172N · Tahlequah, OKThe student pilot’s failure to maintain directional control while landing, which resulted in a runway excursion and nose over.NTSB CEN26LA075Accident · No injuriesClass 4 · LimitedFinal reportSteen Skybolt · Guthrie, OKThe pilot's failure to maintain directional control during landing with a quartering left crosswind.NTSB CEN26LA057Accident · No injuriesClass 4 · LimitedFinal reportZenith Stol CH701 · Weatherford, OKThe pilot’s improper landing flare which resulted in a hard landing. Contributing to the accident was the pilot being in a rush and failing to note the wind direction and speed.NTSB CEN26LA021Accident · No injuriesClass 4 · LimitedFinal reportBeech C23 · Tulsa, OKThe pilot’s improper landing flare which resulted in a hard bounced landing.NTSB CEN26LA002Accident · Minor injuriesClass 4 · LimitedFinal reportChampion 7GC · Haskell, OKThe pilot’s excessive braking during the landing roll, which resulted in a nose over. Contributing to the accident was the pilot’s lack of experience with the recently installed brakes and tundra tires.NTSB CEN25LA350Accident · No injuriesClass 4 · LimitedFinal reportCessna 172R · Ardmore, OKThe pilot’s improper landing flare, which resulted in a hard, bounced landing.NTSB CEN25LA330Accident · Minor injuriesClass 4 · LimitedFinal reportEXP Supercub · Grove, OKThe pilot’s failure to maintain elevator control during the landing, which resulted in a nose over.NTSB CEN25LA201Accident · No injuriesClass 4 · LimitedFinal reportLancair 235 · Pawhuska, OKThe pilot’s failure to properly configure the airplane for landing.NTSB CEN25LA173Accident · No injuriesClass 3 · LimitedPreliminary reportCessna 180F · Duncan, OKOn April 30, 2025, about 1950 central daylight time, a Cessna 180F airplane, N2135Z, sustained substantial damage when it was involved in an accident at the Halliburton Field Airport (DUC), Duncan, Oklahoma. The pilot and passenger were not injured. The…NTSB CEN25LA167Accident · Minor injuriesClass 4 · LimitedFinal reportBell Helicopter Textron Canada 505 · Bethany, OKThe pilot’s improper landing technique that allowed the helicopter’s right skid to get caught on the landing platform, which resulted in a dynamic rollover.NTSB CEN25LA123Accident · Minor injuriesClass 4 · LimitedFinal reportCaldwell C W 162F · Mounds, OKThe student pilot’s failure to maintain control of the helicopter during a precautionary landing, which resulted in a dynamic roll over and postimpact fire.NTSB CEN25LA002Accident · No injuriesClass 4 · LimitedFinal reportAir Tractor AT-402A · Moffett, OKThe tail wheel assembly’s fractured bolt which resulted in the pilot’s loss of directional control during landing.NTSB CEN24LA258Accident · Minor injuriesClass 4 · LimitedFinal reportProgressive Aerodyne Searey · Stillwater, OKThe pilot’s failure to properly configure the landing gear before performing a water landing.NTSB CEN24LA222Accident · No injuriesClass 4 · LimitedFinal reportCessna 172I · Ada, OKThe student pilot’s failure to maintain directional control during landing resulting in a runway excursion and impact with a sign.NTSB CEN24LA219Accident · Serious injuriesClass 4 · LimitedFinal reportSchweizer SGS 1-23H-15 · Chouteau, OKThe student pilot’s failure to maintain control of the glider while landing. Contributing to the accident was the unclear communications between the student pilot and instructor.NTSB CEN24LA180Accident · No injuriesClass 4 · LimitedFinal reportCessna 182 · Davis, OKThe pilot’s failure to maintain proper airspeed on approach which resulted in an extended touchdown, bounced landing, and runway overrun.NTSB CEN24LA130Accident · No injuriesClass 4 · LimitedFinal reportBeech B19 · Oklahoma City, OKThe student pilot’s improper landing flare, which resulted in a bounced landing, aerodynamic stall, and impact with the runway.NTSB CEN24LA122Accident · No injuriesClass 4 · LimitedFinal reportPiper PA32 · Tulsa, OKThe pilot's inadvertent retraction of the flaps while landing which resulted in a hard landing and loss of directional control.NTSB CEN24LA091Accident · No injuriesClass 3 · LimitedFinal reportPiper PA-24 · Hugo, OKThe binding of a main landing gear push-pull cable, which rendered the landing gear inoperative in a partially retracted position. Contributing to the accident was the pilot’s delay in executing a landing, which led to a total loss of engine power due to fuel…NTSB CEN24LA074Accident · No injuriesClass 4 · LimitedFinal reportPiper PA-34-200T · Ponca City, OKThe pilot’s loss of directional control during landing in gusty crosswind conditions.NTSB CEN24LA070Accident · No injuriesClass 4 · LimitedFinal reportHelicopteres Guimbal Cabri G2 · Claremore, OKThe flight instructor’s failure to maintain sufficient rotor speed during a practice autorotation which resulted in a hard landing.NTSB CEN23LA423Accident · 1 fatalClass 3 · LimitedFinal reportBeech A36 · Broken Bow, OKThe pilot’s failure to maintain the runway centerline during landing and subsequent failure to maintain clearance from the airport grounds worker during the landing roll. Contributing to the accident was the absence of a NOTAM for mowing operations at the…NTSB CEN23LA157Accident · Minor injuriesClass 4 · LimitedFinal reportAcro Sport II · Skiatook, OKThe pilot's failure to maintain directional control during landing in a gusting crosswind.NTSB CEN23LA148Accident · No injuriesClass 4 · LimitedFinal reportCessna 550 · Oklahoma City, OKThe pilot’s improper landing flare, which resulted in a hard, bounced landing, runway excursion, and subsequent collision with a runway sign. Contributing to the accident was the pilot’s lack of experience in the airplane, the unstabilized approach, and…NTSB CEN23LA140Accident · No injuriesClass 4 · LimitedFinal reportCessna 170A · Oklahoma City, OKThe pilot’s loss of directional control during landing with wind gusts, which resulted in a runway excursion and nose over.NTSB CEN23LA121Accident · No injuriesClass 4 · LimitedFinal reportAmerican Champion 8KCAB · Oklahoma City, OKThe pilot’s failure to maintain directional control during the landing, that resulted in a runway excursion, and an impact with an obstacle.NTSB CEN23LA117Accident · Minor injuriesClass 4 · LimitedFinal reportLuscombe 8A · Guthrie, OKThe student pilot’s failure to maintain directional control during the landing roll.NTSB CEN23LA075Accident · No injuriesClass 4 · LimitedFinal reportCessna 150 · Yukon, OKThe pilot’s failure to maintain directional control during the landing roll.NTSB CEN23LA055Accident · No injuriesClass 4 · LimitedFinal reportCirrus Design SR22T · Guthrie, OKThe airplane’s collision with a deer on the runway during landing.NTSB CEN22LA411Accident · No injuriesClass 4 · LimitedFinal reportCessna T210L · Atoka, OKThe pilot's failure to land the airplane within the desired touchdown zone, which resulted in a long landing and collision with a fence.NTSB CEN22LA443Accident · No injuriesClass 4 · LimitedFinal reportPiper PA28 · Owasso, OKThe student pilot’s failure to maintain a proper descent rate during the short field landing.NTSB CEN22LA294Accident · No injuriesClass 4 · LimitedFinal reportBell Helicopter Textron Canada 206L-4 · Idabel, OKThe pilot’s failure to apply full power during the practice autorotation recovery, which resulted in a hard landing.NTSB CEN22LA296Accident · No injuriesClass 4 · LimitedFinal reportBaker Eugene L RV6-A · Goldsby, OKThe pilot’s failure to maintain directional control during landing resulting in a runway excursion.NTSB CEN21LA311Accident · Minor injuriesClass 4 · LimitedFinal reportEslinger C W/Eslinger S M Cassutt · Pryor, OKThe pilot’s high flare and failure to execute a go-around which resulted in a hard landing and runway excursion.NTSB CEN21LA218Accident · No injuriesClass 4 · LimitedFinal reportCessna R182 · Tulsa, OKThe pilot’s inability to extend the main landing gear due to incomplete maintenance, which resulted in a partial wheels-up landing and the mechanic’s failure to follow proper maintenance procedures that led to the loss of main landing gear system hydraulic…NTSB CEN21LA153Accident · No injuriesClass 4 · LimitedFinal reportEurocopter EC130 · Tulsa, OKThe pilot’s improper decision to approach the airport and enter a low altitude hover with a gusting quartering tailwind, which resulted in a loss of tail rotor effectiveness during a turn at a low altitude.NTSB CEN21LA074Accident · No injuriesClass 4 · LimitedFinal reportZlin Savage Cub-S · Francis, OKThe pilot’s selection of unsuitable terrain for the landing, which resulted in a nose over when the airplane encountered soft sand during the landing roll.NTSB CEN20CA226Accident · No injuriesClass 4 · Data collectionFinal reportBellanca 17 30 · Talihina, OKThe pilot's failure to maintain control of the airplane during a crosswind landing, which resulted in a hard landing and runway excursion.NTSB CEN20CA152Accident · No injuriesData collectionFinal reportCessna 172 · Enid, OKThe flight instructor's delayed remedial action during a power-off approach and go-around in gusting wind conditions, which resulted in a hard landing, loss of directional control, and a runway excursion onto a field.NTSB CEN20CA074Accident · No injuriesData collectionFinal reportPiper PA32 · Kingfisher, OKThe pilot's improper continuation of a landing in which he landed too far down the runway at too high a speed, which resulted in a loss of directional control and a runway excursion.NTSB GAA19CA554Accident · No injuriesData collectionFinal reportPiper PA32R · Owasso, OKThe pilot's improper altitude and airspeed control during landing, which resulted in the airplane landing long and a subsequent runway overrun and impact with a drainage culvert.NTSB CEN19TA327Accident · No injuriesClass 3Final reportPiper PA60 · Tulsa, OKThe pilot's improper landing flare, which resulted in an aerodynamic stall and hard landing.NTSB CEN19TA328Accident · Serious injuriesClass 3Final reportLindstrand 105A · Lawton, OKA hard landing, which resulted the basket tipping over and a passenger sustaining a serious injury.NTSB GAA19CA512Accident · No injuriesData collectionFinal reportPiper PA28 · Chickasha, OKThe student pilot's failure to maintain crosswind correction during landing and his subsequent loss of directional control during the landing roll, which resulted in a runway excursion and impact with uneven terrain.NTSB CEN19LA264Accident · Serious injuriesClass 3 · LimitedFinal reportCessna 150 · Cordell, OKThe pilot's improper landing flare, which resulted in a hard bounced landing.NTSB GAA19CA368Accident · No injuriesData collectionFinal reportCessna 172 · Tulsa, OKThe pilot's failure to maintain directional control while landing in gusting crosswind conditions, which resulted in a runway excursion and impact with a taxiway sign.NTSB GAA19CA237Accident · No injuriesData collectionFinal reportVans RV 6 · Chandler, OKThe pilot's overapplication of the brakes during landing on a grass runway, which resulted in a nose-over.NTSB CEN19LA068Accident · No injuriesLimited investigationFinal reportAerospatiale AS350 · Ponca City, OKThe pilot's failure to maintain altitude during the hover operation while his view was obstructed due to the fogged-over windshield.