History of Flight
On May 15, 2017, about 1644 Pacific daylight time, an experimental, amateur-built Lancair Evolution, N846PM, was substantially damaged in an accident near Firebaugh, California. The front seat passenger and one rear seat passenger received minor injuries; the private pilot and two other passengers were uninjured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal cross-country flight to return to the home airport.
The pilot reported that while cruising at 25,000 ft, the windshield suddenly "exploded," causing an instant cabin decompression. He activated the oxygen system and donned his oxygen mask. During the subsequent steep descent, the pilot located and navigated to a nearby airport. After turning to the final leg of the traffic pattern, he extended the landing gear but did not receive confirmation that the left main landing gear was extended and locked via the landing gear position indicator lights. After recycling the gear with the same indication, he decided to land with the gear retracted. The airplane touched down smoothly at high speed, overran the runway, impacted a fence, and came to rest in a field about 900 ft beyond the departure end of runway 12. Substantial damage occurred to both wings.
Windshield Examination
Postaccident examination revealed that most of the windshield was broken, with only a few fragments remaining attached to the fuselage frame. The windshield was cast acrylic bonded to a carbon fiber reinforced polymer (CFRP) frame. Three pieces along the lower edge were easily removed from the frame. The frame showed visible damage at the 2, 6, and 10 o'clock positions. The entire windshield frame, including attached composite structure, was sent to Wichita State University's National Institute of Aviation Research (NIAR) for analysis.
NIAR's examination found gaps indicating that portions of the windshield were not fully bonded. However, the manufacturer (Lancair International, Inc.) failed to provide engineering data on the windshield, frame, and adhesive, rendering the analysis inconclusive. NIAR noted extensive cracking directly in front of the windshield, consistent with delaminated wet-layup plies applied after the fuselage halves were joined, indicating significant structural flexing.
Landing Gear
Postaccident testing showed that all three landing gear deployed normally using the bypass valve, but the gear status display showed unsafe indications for the main gear. Photographs revealed that both the left main landing gear down and up position relay modules had been dislodged from their terminals in the avionics bay (located below the windshield on top of the instrument panel). Once the modules were reinstalled, the left main landing gear down indications worked normally.
Laboratory Findings
NIAR performed thermal analysis on the composite frame, acrylic windshield, and paste adhesive. The average low glass transition temperature (Tg) for the paste adhesive was 192°F. At the time of failure, the outside air temperature was -34°C (-29°F), which had been constant for the previous 6 minutes; thus, the windshield frame material was not beyond Tg. Paint evaluation showed low total solar reflectance, indicating higher heat retention, raising concern for potential high temperatures due to the dark paint and the airplane's home airport in Arizona. However, without manufacturer data, the analysis was inconclusive.
The NTSB Materials Laboratory examined the windshield remnants. Fracture analysis identified a longitudinal fracture (A) and a crack (B) in the lower left side. Ratchet marks at the origin of fracture B indicated multiple initiation points on the interior surface, consistent with higher tension stress there. The forward end of fracture B intersected fracture A, but their relationship could not be determined.
Examination of the windshield edge near fracture B revealed gouges inconsistent with the specified sanding procedure (DA sander with 40-grit paper). The Hysol adhesive near fractures A and B showed grinding marks also inconsistent with the specified sanding. Additionally, the fuselage skin layup differed from the construction drawings: the interior skin had 2 more layers than specified, and the exterior skin had 4 more layers than expected. Another section of the frame matched the interior layup but varied in exterior orientations and had 4 additional layers.
All four propeller blades were bent aft. No evidence of a bird strike was found.