# NTSB LAX95LA166: Waco UPF-7, N20971, Chino, CA, April 22, 1995 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: April 22, 1995, 10:51 local (17:51 UTC) - Place: Chino, CA - Coordinates: 33.999164, -117.679374 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.9992&lon=-117.6794&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report November 11, 1996 - Report: Approved by Office Director - NTSB case key (mKey): 29077 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX95LA166 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/29077/pdf - Page: https://openairdocs.org/ntsb/LAX95LA166 ## Probable cause failure of the attachment link for the master cylinder return spring, which allowed the left brake to lock. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Nose over, landing - roll - miscellaneous,bolt/nut/fastener/clamp/spring - failure (cause) - landing gear,normal brake system - locked (cause) ## Analysis THE PILOT EXPERIENCED A DIRECTIONAL CONTROL PROBLEM DURING THE LANDING ROLL. IN HER INITIAL ORAL STATEMENT, SHE INDICATED THE DIFFICULTY WAS DUE TO THE WIND CONDITION. REGARDING HER ATTEMPT TO CONTROL THE AIRCRAFT, SHE SAID SHE THOUGHT SHE MIGHT HAVE INADVERTENTLY APPLIED THE BRAKES, WHICH HAD CAUSED THE AIRCRAFT TO NOSE OVER. A POSTACCIDENT INSPECTION OF THE AIRCRAFT REVEALED THAT THE ATTACHMENT LINK OF THE RETURN SPRING FOR THE LEFT MASTER CYLINDER HAD FAILED. ACCORDING TO THE MAINTENANCE MANUAL FOR THE HAYES NO. D-87-36 BRAKE MASTER CYLINDER, THE ASSEMBLY WAS DESIGNED SO THAT SOME BRAKE FLUID WOULD BE ADDED TO THE PRESSURE SIDE OF THE PISTON DURING THE RETURN STROKE. HOWEVER, IF THE RELIEF PORT WAS NOT OPENED BY A COMPLETE RETURN OF THE PISTON, WHEN THE BRAKE WAS RELEASED, PRESSURE COULD HAVE BUILT UP IN THE SYSTEM, CAUSING THE BRAKE TO DRAG OR LOCK. ## Factual narrative On April 22, 1995, at 1051 hours Pacific daylight time, a Waco UPF-7, N20971, sustained substantial damage when it nosed over while landing at Chino, California. The privately owned and operated aircraft was on a personal solo flight. Visual meteorological conditions prevailed and no flight plan had been filed for the operation. The certificated private pilot was not injured. The flight had originated from the Chino airport at 1030 on the day of the accident. The pilot stated that she planned to perform some touch-and-go landings at the home base airport. She said that the automated terminal information service (ATIS) "information Lima" was reporting runway 08 as the active runway with the winds from 090 degrees at 10 knots gusting to 20 knots. According to Chino Air Traffic Control Tower (ATCT) information, the pilot was cleared for takeoff at 1046 hours. During the takeoff roll, the wind direction reversed to 290 degrees at 6 knots. At 1105, a terminal observation reported the wind as 270 degrees at 10 knots. According to the pilot, she received amended pattern instructions during her takeoff roll. She was requested to make a south departure and to reenter the pattern on a downwind for runway 26. During the landing roll, she stated that she experienced directional control problems due to wind conditions. During her attempt to control the aircraft, she said she believed she had inadvertently applied the brakes which had caused the aircraft to nose over. A postaccident inspection of the aircraft conducted by the owner's mechanic revealed that the attachment link of the return spring for the left master cylinder had separated. According to the maintenance manual for the Hayes No. D-87-36 brake master cylinder, the assembly is designed so that some brake fluid is added to the pressure side of the piston during the return stroke. However, if the relief port is not opened by a complete return of the piston when the brake is released, pressure can build up in the system, causing the brake to drag or lock. ## Aircraft - Registration: [N20971](https://openairdocs.org/aircraft/N20971), registered now, S/N 5317, built 1940 (OpenAirDocs) - Reported make and model: WACO UPF-7 - Registry model: [Waco UPF-7](https://openairdocs.org/model/waco-upf-7) (registry code 9601302) (OpenAirDocs) - Registry engine: [Continental W670-6N](https://openairdocs.org/engine/continental-w670-6n) (registry code 17318, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 5317 - Engines: CONTINENTAL W670 220 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Gruenwald,Sherry D. Conser. - Airworthiness certificate: Standard, Normal - Last inspection: Annual, December 23, 1994, 13 hours before - Departed: CNO - Airport: CNO, Chino, runway 8, 4,856 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 48; private; airplane ratings: single-engine land; medical: class 3, valid medical--w/ waivers/lim; seat: rear; flight hours: 674 total, 620 in this make and model, 565 as pilot in command, 16 in the last 90 days, 1 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 10 knots - Visibility: 50 statute miles - Lowest ceiling: none - Altimeter: 30.00 inHg - Observed at: CNO ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19950422011009A](https://openairdocs.org/incident/19950422011009A), Apr 22, 1995: Waco UPF7, Chino, CA, Substantial damage. Nosed over landing. Pilot beleived she hit brakes but inspection of brakes showed return spring broke locked brake. ## Other investigations on N20971 (1) 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. - [NTSB UNK64X0433](https://openairdocs.org/ntsb/UNK64X0433), Feb 2, 1964: Waco UPF7 (N20971), San Fernand, CA, substantial damage 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. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.