# NTSB WPR21LA040: Schleicher ASW20C, N18MA, Clayton, CA, November 7, 2020

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Class 4 · Limited · Final report
- Date: November 7, 2020, 12:51 local (20:51 UTC)
- Place: Clayton, CA · Mt. Diablo State Park
- Coordinates: 37.839997, -121.87482 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=37.8400&lon=-121.8748&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Defining events: [Maneuvering: Midair collision](https://openairdocs.org/ntsb-events/250); [Maneuvering: Midair collision](https://openairdocs.org/ntsb-events/250)
- Highest injury: Serious injuries
- Injuries: 2 serious
- Status: Completed
- Report: Approved by Office Director
- Investigation class: Class 4 - Basic report with no Prelim publish
- NTSB office: Western Pacific Region
- Parties: FAA
- NTSB case key (mKey): 102252
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR21LA040
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/102252/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=102252
- Page: https://openairdocs.org/ntsb/WPR21LA040

## Probable cause (aircraft 1)

The failure of both pilots of each glider to see an avoid one another while maneuvering, which resulted in a mid-air collision.

## Findings

NTSB's coded findings; those marked are part of the probable cause.

- [Object/animal/substance: aircraft](https://openairdocs.org/ntsb-findings/03022040): Environmental issues › Physical environment · Effect on equipment, aircraft 1; cases with it: [Schleicher ASW-20C, 1 case](https://openairdocs.org/ntsb-findings/03022040/cases.md?model=3801502), [All aircraft, 116 cases](https://openairdocs.org/ntsb-findings/03022040/cases.md)
- [Attention/monitoring: monitoring other aircraft](https://openairdocs.org/ntsb-findings/02021540): Personnel issues › Psychological · Pilot (probable cause), aircraft 1; cases with it: [Schleicher ASW-20C, 1 case](https://openairdocs.org/ntsb-findings/02021540/cases.md?model=3801502), [All aircraft, 231 cases](https://openairdocs.org/ntsb-findings/02021540/cases.md)
- [Object/animal/substance: aircraft](https://openairdocs.org/ntsb-findings/03022040): Environmental issues › Physical environment · Effect on equipment, aircraft 2; cases with it: [Schleicher ASW-27, 1 case](https://openairdocs.org/ntsb-findings/03022040/cases.md?model=3801501), [All aircraft, 116 cases](https://openairdocs.org/ntsb-findings/03022040/cases.md)
- [Attention/monitoring: monitoring other aircraft](https://openairdocs.org/ntsb-findings/02021540): Personnel issues › Psychological · Pilot (probable cause), aircraft 2; cases with it: [Schleicher ASW-27, 2 cases](https://openairdocs.org/ntsb-findings/02021540/cases.md?model=3801501), [All aircraft, 231 cases](https://openairdocs.org/ntsb-findings/02021540/cases.md)

## Sequence of events

The events NTSB coded, in order, by phase of flight. The defining event best describes what happened.

- [Maneuvering: Midair collision](https://openairdocs.org/ntsb-events/250) (defining event), aircraft 1; cases with it: [Schleicher ASW-20C, 1 case](https://openairdocs.org/ntsb-events/250/sequence.md?model=3801502), [All aircraft, 196 cases](https://openairdocs.org/ntsb-events/250/sequence.md)
- [Maneuvering: Midair collision](https://openairdocs.org/ntsb-events/250) (defining event), aircraft 2; cases with it: [Schleicher ASW-27, 2 cases](https://openairdocs.org/ntsb-events/250/sequence.md?model=3801501), [All aircraft, 196 cases](https://openairdocs.org/ntsb-events/250/sequence.md)

## Analysis (aircraft 1)

The pilot of an ASW-20C glider reported that, while following lift under cumulus clouds, he observed another glider, an ASW-27 traversing from right to left. He entered into a steep dive in an attempt to avoid the other glider, however, the ASW-20C impacted the ASW-27 glider. Following the collision, the ASW-20C entered a steep descent and rolled inverted before the pilot elected to bail out and parachute to safety. The ASW-20C pilot added that the glider was equipped with a FLARM collision system, and prior to the collision, did not receive any alerts of additional traffic. The pilot of an ASW-27 glider reported that while maneuvering, another glider suddenly appeared to his left and followed by a collision. The pilot stated that his glider immediately entered a descent and was out of control. The pilot of the ASW-27 subsequently bailed out and parachuted to safety. The glider was equipped with a FLARM collision system but was inoperative awaiting an annual software update. The ASW-20C glider sustained substantial damage to the left wing. The ASW-27 glider sustained substantial damage to the left wing and aft fuselage. Both glider pilots reported that there were no preaccident mechanical failures or malfunctions with the gliders that would have precluded normal operation.

## Aircraft 1

- Registration: [N18MA](https://openairdocs.org/deregistered/N18MA-2022-10-27), registration cancelled 2022-10-27, S/N 20844, built 1986 (OpenAirDocs)
- Reported make and model: SCHLEICHER ASW20C
- Registry model: [Schleicher ASW-20C](https://openairdocs.org/model/schleicher-asw-20c) (registry code 3801502) (OpenAirDocs)
- Registry engine: [NONE](https://openairdocs.org/engine/none) (registry code 00000, none) (OpenAirDocs)
- Category: Glider
- Serial number: 20844
- Year built: 1986
- Airframe hours: 1431.7
- Damage: Substantial damage
- Flight: Personal, Part 91
- Registered owner: Paul N Loewenstine
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Annual, February 22, 2020
- Departed: C83, Byron, CA
- Equipment: ADS-B, Satellite tracking device, Data recorder, Electronic flight bag or handheld device

## Aircraft 2

- Registration: [N81KP](https://openairdocs.org/aircraft/N81KP), registered now, S/N 27041, built 1997 (OpenAirDocs)
- Reported make and model: SCHLEICHER ASW27
- Registry model: [Schleicher ASW-27](https://openairdocs.org/model/schleicher-asw-27) (registry code 3801501) (OpenAirDocs)
- Registry engine: [NONE](https://openairdocs.org/engine/none) (registry code 00000, none) (OpenAirDocs)
- Category: Glider
- Serial number: 27041
- Year built: 1997
- Airframe hours: 4245
- Damage: Substantial damage
- Flight: Personal, Part 91
- Registered owner: Laurance J Suter
- Airworthiness certificate: Standard, Normal; Standard, Utility
- Last inspection: Annual, March 3, 2020
- Departed: C83, Byron, CA
- Equipment: Handheld GPS

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot, aircraft N18MA; age 71; injuries: minor; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: basicmed, with waivers/limitations; last flight review February 7, 2020; seat: single; restraint: 4-point; flight hours: 1,847 total, 186 in this make and model, 1,800 as pilot in command, 31 in the last 90 days, 10 in the last 30 days, 5 in the last 24 hours
- Pilot, aircraft N81KP; age 73; injuries: serious; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: basicmed, with waivers/limitations; last flight review February 9, 2020; seat: center; restraint: 4-point; flight hours: 2,794 total, 2,723 as pilot in command, 31 in the last 90 days, 7 in the last 30 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: variable at 5 knots
- Visibility: 10 statute miles
- Temperature: 61 °F, dew point 32 °F
- Altimeter: 29.73 inHg
- Turbulence: Moderate
- Observed at: KLVK, 11 nm away

## FAA reports on this event (2)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 20201107020572A](https://openairdocs.org/incident/20201107020572A), Nov 7, 2020: Schleicher ASW-20C, Walnut Creek, CA, Substantial damage. Walnut Creek, CA: mid-air collision reported by ntsb/hicks @ 2038PST when N81KP, Schleicher and N18MA, Schleicher collided. N81KP and N18MA gliders collided…
- [Accident 20201107020582A](https://openairdocs.org/incident/20201107020582A), Nov 7, 2020: Schleicher ASW-27, Walnut Creek, CA, Substantial damage. Walnut Creek, CA: mid-air collision reported by ntsb/hicks @ 2038PST when N81KP, Schleicher and N18MA, Schleicher collided. N81KP and N18MA gliders collided…

## Docket (4 files)

The files NTSB released with the investigation on August 20, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=102252. 7.3 MB in all.

- N18MA pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11630401&FileExtension=pdf&FileName=Loewenstein%206120%20Pilot%20Operator%20Aircraft%20Accident%20Incident_Redacted-Rel.pdf
- N81KP pilot/operator aircraft accident report, NTSB form 6120.1 (item 2, PDF, 9 pages, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11631145&FileExtension=pdf&FileName=Suter%206120%20Pilot%20Operator%20Aircraft%20Accident%20Incident_Redacted-Rel.pdf
- Record of phone conversation (N18MA pilot) (item 3, PDF, 1 page, 159 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11633304&FileExtension=pdf&FileName=Record%20of%20phone%20conversation%20(N18MA%20Pilot)-Rel.pdf
- Damage photos (item 4, PDF, 3 pages, 3.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11631550&FileExtension=pdf&FileName=Damage%20Photos-Rel.pdf

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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