NTSB investigations, 2006
51 cases where the phase of flight was Taxi.
Cases per year
| 1962 | 6 |
|---|---|
| 1963 | 6 |
| 1964 | 346 |
| 1965 | 306 |
| 1966 | 372 |
| 1967 | 381 |
| 1968 | 215 |
| 1969 | 200 |
| 1970 | 212 |
| 1971 | 189 |
| 1972 | 181 |
| 1973 | 177 |
| 1974 | 169 |
| 1975 | 179 |
| 1976 | 151 |
| 1977 | 156 |
| 1978 | 184 |
| 1979 | 134 |
| 1980 | 132 |
| 1981 | 113 |
| 1982 | 127 |
| 1983 | 104 |
| 1984 | 96 |
| 1985 | 73 |
| 1986 | 70 |
| 1987 | 87 |
| 1988 | 83 |
| 1989 | 73 |
| 1990 | 74 |
| 1991 | 49 |
| 1992 | 55 |
| 1993 | 60 |
| 1994 | 51 |
| 1995 | 56 |
| 1996 | 59 |
| 1997 | 64 |
| 1998 | 65 |
| 1999 | 55 |
| 2000 | 57 |
| 2001 | 57 |
| 2002 | 62 |
| 2003 | 49 |
| 2004 | 48 |
| 2005 | 52 |
| 2006 | 51 |
| 2007 | 49 |
| 2008 | 64 |
| 2009 | 45 |
| 2010 | 41 |
| 2011 | 45 |
| 2012 | 41 |
| 2013 | 44 |
| 2014 | 33 |
| 2015 | 43 |
| 2016 | 38 |
| 2017 | 45 |
| 2018 | 50 |
| 2019 | 51 |
| 2020 | 25 |
| 2021 | 47 |
| 2022 | 52 |
| 2023 | 48 |
| 2024 | 45 |
| 2025 | 58 |
| 2026 | 48 |
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 year(c.\"eventDate\") = 2006
AND c.\"mKey\" IN (SELECT case_mkey FROM case_phases WHERE main = 250)
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 year(c."eventDate") = 2006
AND c."mKey" IN (SELECT case_mkey FROM case_phases WHERE main = 250)
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 LAX07LA064Accident · No injuriesLimited investigationFinal reportBoeing 737-7H4 · San Diego, CAFailure of the captain of the other taxiing airplane to maintain clearance from an occupied airplane stopped on the ramp.NTSB DFW07LA056Accident · No injuriesLimited investigationFinal reportCessna 172S · Tulsa, OKThe pilot's failure to maintain clearance from a hangar and parked airplane during the unauthorized use of an airplane.NTSB MIA07IA031Incident · No injuriesIncident investigationFinal reportBoeing 747-436 · Miami, FLThe flightcrew's misinterpretation of available lighting, signage, and airfield marking cues during taxi.NTSB MIA07LA026Accident · No injuriesLimited investigationFinal reportLingwall Rebich-Pitts · Naples, FLThe experimental airplane's pilot inadequate visual lookout while taxiing for takeoff, which resulted in an on-ground collision with a Piper airplane which was standing with its engine operating in the runup area.NTSB SEA07LA026Accident · No injuriesLimited investigationFinal reportCessna 310B · Lake Stevens, WAThe collapse of the main landing gear for an undetermined reason while taxiing from landing.NTSB CHI07CA033Accident · No injuriesData collectionFinal reportCessna C-425 · Menominee, MIThe pilot failed to maintain control of the aircraft while parking the aircraft, and failed to maintain clearance from the building as the airplane taxied forward. A factor was the terminal.NTSB NYC07CA050Accident · No injuriesData collectionFinal reportCessna 152 · Block Island, RIThe pilot's failure to maintain adequate clearance while taxiing, which resulted in a collision with a construction vehicle. A factor in this accident was the location of the construction vehicle, which was parked on the ramp, adjacent to the parking area.NTSB ATL07LA016Accident · No injuriesLimited investigationFinal reportBoeing 717-200 · Memphis, TNThe captain's inadequate visual look out during taxi.NTSB CHI07LA021Accident · No injuriesLimited investigationFinal reportBoeing 717-200 · Milwaukee, WIThe failure of ground personnel to verify the clearance between the airplanes prior to signaling the crew tha the crew of the other airplane that they were cleared to taxi.NTSB CHI07FA020Accident · No injuriesField investigationFinal reportAirbus A-320-200 · Chicago, ILThe pilot-in-command of the other airplane failed to maintain clearance with the parked airplane during taxi for takeoff.NTSB NYC07LA017Accident · No injuriesLimited investigationFinal reportBoeing 747-400 · Newark, NJThe failure of the Boeing 747 crew to maintain an adequate visual lookout. Contributing to the accident were the night lighting conditions, the back lighting from the apron lights, and the crew's diverted attention in focusing on a Boeing 757 that they were…NTSB LAX07IA008Incident · No injuriesIncident investigationFinal reportGulfstream G1159B · Burbank, CAThe pilot's improper decision to continue to taxi onto an unusable taxi area clearly marked as such. A finding in the accident was the incorrectly depicted EMAS area on the approach chart.NTSB SEA07LA011Accident · No injuriesLimited investigationFinal reportSorensen Searey · Marysville, WAThe pilot's failure to identify an unsafe condition (strong tidal currents) prior to a water landing, which resulted in the airplane nosing over when the pilot was unable to maintain aircraft control.NTSB SEA07LA004Accident · No injuriesLimited investigationFinal reportCessna 182M · Boise, IDThe pilot's failure to maintain adequate clearance while taxiing. A contributing factor was the temporary construction fence next to the taxiway.NTSB NYC06LA222Accident · No injuriesLimited investigationFinal reportAirbus Industrie A319-112 · New York, NYThe Airbus first officer's misjudged clearance from the EMB-170. Also causal was the ground controller's decision to issue a taxi clearance for the Airbus to pass behind the EMB-170. A factor to the accident was the light condition.NTSB DFW06CA206Accident · No injuriesData collectionFinal reportBeech B200 · Hondo, TXThe collision with an unmarked pothole in the taxiway while taxiing for departure. A contributing factor was the obscuration by water.NTSB DCA06MA064Accident · 49 fatalClass 1 · MajorFinal reportBombardier CRJ-100 · Lexington, KYthe flight crewmembers's 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. Contributing to the…NTSB LAX06IA301Incident · No injuriesIncident investigationFinal reportMcDonnell Douglas DC-9-83 · Long Beach, CAThe over wing heater blanket wiring installation that had chaffed and arced, which produced an electrical smell in the cabin area.NTSB ANC06LA113Accident · Serious injuriesLimited investigationFinal reportSeales Protech PT-2B · Crestview, FLThe pilot's failure to correct for torque/p-factor during takeoff initial climb, which resulted in a loss of control and a collision with trees and a power line. Factors contributing to the accident were the pilot's lack of familiarity with the airplane, and…NTSB CHI06CA279Accident · No injuriesData collectionFinal reportMeyers MAC-145 · Manistique, MIThe pilot not verifying the landing gear selector position prior to starting the taxi.NTSB SEA06CA151Accident · No injuriesData collectionFinal reportCessna 180H · Hailey, IDThe pilot's failure to maintain directional control of the airplane during taxi, which resulted in a nose over. A factor was the wind gust condition.NTSB CHI06FA206Accident · 1 fatalField investigationFinal reportGrumman TBM-3 · Oshkosh, WIThe Avenger pilot's visual lookout was inadequate and he failed to maintain clearance from the RV-6. Contributing factors were the Avenger's restricted visibility and the RV-6.NTSB ANC06LA095Accident · No injuriesLimited investigationFinal reportde Havilland DHC-2 · Big Lake, AKThe pilot's failure to maintain control of the airplane while step taxiing a float-equipped airplane, which resulted in a collision with an embankment. A factor contributing to the accident was an unfavorable wind.NTSB MIA06LA130Accident · No injuriesLimited investigationFinal reportCessna 550 · Marathon, FLThe separation for undetermined reasons of the stud (P/N 6541204-5) which secures the main landing gear actuator assembly side brace to the main landing gear outer cylinder, allowing partial collapse of the right main landing gear while taxiing after landing.NTSB CHI06CA181Accident · No injuriesData collectionFinal reportPiper PA-31-350 · Indianapolis, INThe failure of the tug driver to maintain clearance from the airplane taxiing on an active taxiway. A factor was the night conditions.NTSB CHI06LA161Accident · No injuriesLimited investigationFinal reportBoeing 737-300 · New York, NYThe foreign object damage to the horizontal stabilizer during taxi as a result of improper airport maintenance by contract maintenance personnel. The aluminum plate was a factor.NTSB DEN06CA082Accident · No injuriesData collectionFinal reportCessna 182R · Albuquerque, NMthe pilot's failure to maintain directional control of the airplane after landing.NTSB ANC06LA070Accident · No injuriesLimited investigationFinal reportPiper PA-18-150 · Birchwood, AKThe pilot's improper servicing/adjustment of the main landing gear brakes, which resulted in a locked brake and a loss of control while taxiing.NTSB SEA06TA118Accident · No injuriesFinal reportCessna 206H · Aurora, ORThe failure of both the pilot of the aircraft traveling on a taxi lane and the operator of the automobile driving on a taxi lane to maintain an adequate visual lookout and their failure to see and avoid one another.NTSB DFW06CA143Accident · No injuriesData collectionFinal reportTaylorcraft BC12-D · Justin, TXThe pilot's improper compensation for the prevailing high wind conditions.NTSB DEN06CA078Accident · No injuriesData collectionFinal reportAviat A-1A · Englewood, COthe pilot's failure to maintain aircraft control while taxiing from landing, resulting in a collision with a refuse dumpster. A contributing factor was his physical impairment by alcohol.NTSB CHI06CA134Accident · No injuriesData collectionFinal reportPiper PA-28-161 · Grayslake, ILThe student pilot's failure to maintain clearance from the parked vehicle during taxi and the flight instructor's inadequate operational oversight. A factor to the accident was the parked vehicle.NTSB LAX06LA154Accident · No injuriesLimited investigationFinal reportBombardier CL-600-2D24 · Las Vegas, NVThe failure of ground service personnel to properly set the parking brake on the lead baggage cart.NTSB LAX06CA157Accident · No injuriesData collectionFinal reportCessna 172S · Big Bear, CAthe pilot's failure to maintain wing clearance from a pole during taxi.NTSB SEA06CA098Accident · No injuriesData collectionFinal reportCessna 172N · Billings, MTThe pilot's failure to maintain clearance from a sign while taxiing to parking.NTSB DEN06IA068Incident · No injuriesIncident investigationFinal reportBoeing 747-400 · Denver, COThe ground crew's failure to retract the adjacent jetway and to verify the airplane's clearance with the jetway as it taxied.NTSB DEN06LA070Accident · No injuriesLimited investigationFinal reportCessna T-R182RG · Englewood, COthe pilot inadvertently retracting the landing gear.NTSB SEA06CA073Accident · No injuriesData collectionFinal reportCessna 170B · Havre, MTThe pilot's improper starting procedures in attempting to hand-prop the airplane's engine. Contributing factors were the discharged battery, the failure of the right parking brake and the hangar which the aircraft collided with.NTSB MIA06CA102Accident · No injuriesData collectionFinal reportPiper 38-112 · Apopka, FLThe pilot's failure to maintain clearance from an object while taxiing which resulted in the airplane impacting the object and incurring damage.NTSB SEA06CA066Accident · No injuriesData collectionFinal reportCessna 182D · Sandpoint, IDThe pilot's failure to maintain clearance from an object (snow blowing equipment) while taxiing. The snow blowing equipment, and the pilot's failure to adequately maneuver the aircraft around snow berms were factors.NTSB DFW06CA085Accident · No injuriesData collectionFinal reportCessna 182 · Houston, TXThe pilot's failure to maintain directional control while taxiing. A contributing factor was the gusty winds.NTSB ANC06LA024Accident · No injuriesLimited investigationFinal reportCessna 185 · Ely, NVThe pilot's inadequate compensation for a quartering tailwind while taxiing, which resulted in a loss of control and an on ground encounter with terrain. A factor in the accident was the quartering crosswind.NTSB ANC06LA023Accident · No injuriesLimited investigationFinal reportPiper PA-24 · La Vern, CAThe pilot's excessive taxi speed while turning, which resulted in an on ground collision with a taxiway light and the ground.NTSB LAX06CA139Accident · No injuriesData collectionFinal reportBeech G35 · Flagstaff, AZthe pilot's failure to maintain an adequate clearance with obstructions while taxiing.NTSB LAX06CA122Accident · No injuriesData collectionFinal reportCessna 172P · Sedona, AZThe pilot's failure to maintain an adequate clearance from obstructions and diverted attention while taxiing.NTSB CHI06LA089Accident · No injuriesLimited investigationFinal reportBeech 95-55 · Sikeston, MOThe inadvertent landing gear retraction by the pilot during an after landing taxi.NTSB ANC06CA019Accident · No injuriesData collectionFinal reportKenetic Mountain Goat · Palmer, AKThe pilot's selection of unsuitable terrain for taxi, which resulted in the airplane nosing over while taxiing after landing. A factor associated with the accident was the rough and uneven terrain.NTSB LAX06LA108Accident · No injuriesLimited investigationFinal reportCessna 172N · Sacramento, CAthe failure of the pilot of the other airplane to maintain an adequate clearance from obstacles while taxiing.NTSB LAX06LA101Accident · No injuriesLimited investigationFinal reportCessna R182 · Bullhead City, AZoverload of the nose landing gear actuator attach bracket resulting in collapse of the nose gear while taxiing. It is undetermined when and under what circumstances the overload occurred.NTSB DFW06LA057Accident · No injuriesLimited investigationFinal reportAgusta A109E · Fort Worth, TXThe pilot's inadvertent encounter with ground resonance which resulted in the destruction of the helicopter.