Sunday, September 15, 2019

Cirrus SR20, N8160C: Accident occurred May 02, 2019 at Mineral Wells Airport (KMWL), Texas

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Irving, Texas

Aviation Accident Preliminary Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

Arrive Aviation LLC

https://registry.faa.gov/N8160C

Location: Mineral Wells, TX
Accident Number: CEN19LA133
Date & Time: 05/02/2019, 1702 CDT
Registration: N8160C
Aircraft: Cirrus SR20
Injuries: 2 None
Flight Conducted Under: Part 91: General Aviation - Personal

On May 2, 2019, about 1702 central daylight time, a Cirrus SR20 airplane, N8160C, had an infight separation of the right aileron while on final approach to runway 31 at Mineral Wells Airport (MWL), Mineral Wells, Texas. The airline transport pilot and his passenger were uninjured, and the airplane was substantially damaged. The airplane was registered to and operated by Arrive Aviation LLC as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. Day visual meteorological conditions prevailed, and no flight plan was filed for the cross-country flight that departed Fort Worth Meacham International Airport (FTW) about 1630 with the intended destination of Parker County Airport (WEA), Weatherford, Texas.

The pilot reported that he had intended to fly direct to WEA; however, while en route he diverted to MWL to avoid some weather and practice landings. The pilot stated that he completed 3 uneventful landings on runway 31 at MWL, and that while on the downwind leg for his fourth landing he felt the airplane "shudder briefly" shortly before he turned onto a base leg. After the brief shudder, the pilot and the passenger saw the right aileron "fluttering" and the pilot immediately entered left turn to intercept the final approach to runway 31. The pilot said that after aligning with final approach the right aileron separated from the wing about ½ mile from the runway. The pilot reported that he still had roll control of the airplane after the right aileron separated and that an uneventful landing was completed on runway 31.

According to the Cirrus SR20 Illustrated Parts Catalog, the right aileron is attached to the wing by two NAS6203 bolts that pass through two hinge supports (one inboard, one outboard) that are attached to the wing rear spar. Each hinge bolt passes through a spherical bearing housed in its respective hinge support and is threaded into a nut plate that is riveted to an attachment bracket that is bolted to the aileron spar. The inboard and outboard hinge bolts are torqued to between 20-25 inch-pounds. Each hinge bolt head is safety wired to a tab that is riveted to the aileron.

A postaccident examination of the airplane revealed that the entire right aileron had departed the wing during flight. The inboard hinge bolt remained attached through the inboard hinge support and spherical bearing with the appropriate washers and spacer present; however, the inboard hinge bolt had backed out of the nut plate riveted to the inboard attachment bracket (the inboard attachment bracket remained bolted to the separated aileron). The inboard hinge bolt threads were not galled or stripped, and the safety wire holes on the bolt head appeared undamaged. The inboard hinge bolt head did not have any safety wire installed. The hinge bolt moved freely in the spherical bearing, and there was no evidence of corrosion, stepping, or galling to the unthreaded portion. The outboard hinge bolt remained attached to its respective hinge bracket and support. The outboard hinge bolt remained engaged with its respective nut plate; however, the outboard hinge bracket had fractured in overstress. There was safety wire installed between the outboard hinge bolt head and its respective safety wire tab. The outboard safety wire tab was twisted, bent, and fractured, consistent with an overload separation.


Figure 1. Right Aileron, Inboard Hinge Bolt

Figure 2. Right Aileron, Outboard Hinge Bolt

The right aileron was found in one piece along the final approach path to runway 31 in a wooded area about ½ mile from the approach end of runway 31 at MWL. The outboard attachment point was compacted with grass and mud and the outboard trailing edge corner bent. The remaining surfaces of the aileron were relatively straight with minor scratches. The aileron actuation arm, part number (p/n) 15352-001, remained attached to the inboard attachment bracket, p/n 15123-002, though an AN3H22A bolt with the appropriate washers, spacer, and bearings. The AN3H22A bolt was safety wired to the inboard attachment bracket.

The inboard attachment bracket remained bolted to the aileron spar and appeared undamaged. The nut plate remained riveted to the bracket. The inboard safety wire tab remained riveted to the aileron, and a double-twisted strand of 0.032-inch safety wire was found attached to the tab. The safety wire was fractured at the contact point where it would enter the inboard hinge bolt head. The safety wire appeared to be over-twisted, with at least 9 twists observed in the 0.5-inch segment that remained attached to the tab. The Cirrus SR20 Maintenance Manual specifies that 0.032-inch safety wire be installed with 6-12 twists per one inch. The inboard hinge bolt with associated washers and spacer, the inboard attachment bracket with riveted nut plate, and the fractured safety wire with attached tab were retained for additional laboratory examination.


Figure 3. Right Aileron, Inboard Attachment Bracket and Safety Wire with Riveted Tab

Figure 4. Right Aileron, Inboard Hinge Bolt Safety Wire and Riveted Tab With Scale 

A postaccident review of the aircraft maintenance records show the last maintenance performed was an annual inspection completed on November 1, 2018, about 15 flight hours before the accident. According to the logbook entry for the annual inspection, the mechanic had "lubricated control surface rod ends & hinges." The aviation mechanic who completed the annual inspection told a Federal Aviation Administration (FAA) Maintenance Inspector that he had followed the Cirrus SR20 Annual Inspection Checklist. The mechanic also stated that he did not remove any of the aileron hinge bolts during the annual inspection, and that he observed safety wire installed on the aileron hinge bolts. There is no task in the Cirrus SR20 Annual Inspection Checklist that requires removal of the aileron to complete the annual inspection. The airplane had accumulated 2,108.8 hours since it was manufactured in 2003.

Aircraft and Owner/Operator Information

Aircraft Make: Cirrus
Registration: N8160C
Model/Series: SR20 No Series
Aircraft Category: Airplane
Amateur Built: No
Operator: Arrive Aviation LLC
Operating Certificate(s) Held: None

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: MWL, 974 ft msl
Observation Time: 1653 CDT
Distance from Accident Site: 1 Nautical Miles
Temperature/Dew Point: 20°C / 14°C
Lowest Cloud Condition: Clear
Wind Speed/Gusts, Direction: 12 knots / , 260°
Lowest Ceiling: None
Visibility:  10 Miles
Altimeter Setting: 29.93 inches Hg
Type of Flight Plan Filed: None
Departure Point: Fort Worth, TX (FTW)
Destination: Weatherford, TX (WEA)

Wreckage and Impact Information

Crew Injuries: 1 None
Aircraft Damage: Substantial
Passenger Injuries: 1 None
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 2 None
Latitude, Longitude: 32.770833, -98.042778

7 comments:

Anonymous said...

Yikes, glad it all ended well.

Anonymous said...

Since everyone is OK, I would guess it would be important to know if the aileron were ever removed, for any reason.

Additionally, it would be interesting to determine whether or not the flaps were ever extended over the "Vfe" speed of 104kt (50%) or 104kt (100%)..... as if someone would admit to that.

Anonymous said...

The use of wire locking tools is a recipe for age hardening of locking wire due to over twisting,better to wire lock by hand and use feel to determine if the wire is being over stressed,yes it takes a bit longer and is a real art to keep things neat but it avoids situations like this.
I have a feeling this is not the first aileron detachment on a Cirrus ( checking aviation database)either way it is serious enough to look into more deeply,a lucky escape in this case.

Anonymous said...

https://www.youtube.com/watch?v=96EM1JvvZ8s
Safety Wire by Hand

Anonymous said...

When I was in the Army they would not let us use safety wire pliers. Everything was by hand.

Anonymous said...

Terrific composure. Well done.

Anonymous said...

Has anyone heard of an incident like this ... an aileron FALLING OFF an airplane while IN FLIGHT?? I haven't.

Incredible composure on the part of the pilot. Not only was the problem severe. It's surreal to think this particular problem would even occur. Regardless, he flew the airplane. No need for panic. Land the airplane. No problem. No sweat.

Incredible outcome.