NTSB Factual Report

HISTORY OF FLIGHT

On June 16, 2001, about 0945 central daylight time, an experimental exhibition Potez-Air Fouga CM 170, N301FM, piloted by an airline transport pilot, was destroyed on impact with terrain and post impact fire following an in-flight break up while maneuvering in runway 21's pattern at La Crosse Municipal Airport (LSE), near La Crosse, Wisconsin. The business flight was operating under 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The pilot and rear seat passenger were fatally injured. The local flight originated from LSE about 0938, and was on the upwind portion of runway 21's pattern at the time of the accident.

Sponsorship forms for The Deke Slayton Airfest 2001 that was held on June 16 and 17, 2001 at LSE, listed the "[pilot's name] Fouga Jet" as an air show performer.

About 0943, the accident airplane was given a clearance from the LSE Air Traffic Control Tower (ATCT) for a low approach runway 21.

A Federal Aviation Administration (FAA) Inspector interviewed the LSE ATCT Chief. The FAA's record of interview with the Chief stated "that when the aircraft was in front of the tower he first noticed a short vapor trail coming from the left wing tip and shortly thereafter the wing tip tank separated."

The airplane's crew chief stated:

Aircraft departed runway[,] retracted landing gear, made left

turns to remain in the pattern. Base to final turn was to the left at

[approximately] 60 [degrees] bank ([approximately] 7 [minutes]

after start up) [and] then flew over the runway followed by a pull

up of less than 2g's. At the [beginning] of the pull up the left tank

separated from the aircraft.

A retired airline pilot stated:

Observed aircraft fly over the runway at about 1000'. [Aircraft] may

have started a turn downwind (no abrupt maneuvering). Something

long [and ] narrow came off the [Aircraft], hit the left v-tail. Shortly the

[right] tail plane came off.

A US Army Parachute Team member stated:

At approximately midway down the runway the aircraft began a

5 to 10 degrees climb at which point I observed the left wing tip fuel

tank and what appeared to be a small section of the wing separate

from the aircraft and smash through the tail section, which also

became separated.

An Aviation Medical Examiner stated:

Out of the corner of my eye I saw the Fouga making a pass along

runway 21 at about 300 feet A.G.L [above ground level]. Just before the airplane

passed abeam of me I saw that the left wing tank had separated and

was falling in an approximately level attitude. It was not tumbling.

I ... saw the Fouga start to pitch up and all kinds of parts suddenly

separate upward from the top of it. Some of them were rectangular

in shape. There was also a fuel mist visible streaming upward. The

separation was quite violent. Almost immediately the left wing

separated upward and sailed upward. The tail surfaces, I think,

separated at about this time. I'm not sure when the right tank

separated. The fuselage spiraled upward ball for a little while and

then descended almost vertically. It impacted almost vertically,

nose down, with the right wing pointing approximately south.

The FAA Air Show Monitor stated:

The aircraft in my prospective was about 400 to 600' above the

ground [and] breaking up into numerous pieces. I could see that it

was a Fouga jet. The aircraft continued without its left wing and

fell to the ground in a falling leaf manner. The aircraft dropped out

of sight because of the hangers, that blocked my view. I heard the

aircraft hit the ground [and] with the engines still running. The

engines were still running after impact. Then there was black

smoke rising above the hangers and the engine noise ceased.

PERSONNEL INFORMATION

The pilot held an airline transport pilot certificate with an airplane multiengine land rating, commercial privileges for single-engine land airplanes, and private pilot privileges for single-engine sea airplanes. He was issued a first-class medical certificate on October 3, 2000, with limitations for corrective lenses. On the application for that flight physical, the pilot reported that he had accumulated 3,200 total flight hours and reported he had flown 100 hours in the past 6 months.

AIRCRAFT INFORMATION

The accident airplane, N301FM, was a Potez-Air Fouga CM 170, Magister, serial number 240. The CM 170 is an all metal, medium-wing, twin-engine airplane with retractable tricycle landing gear. It has two tandem cockpits. The tail unit is v-shaped. Two Turbomeca Marbore VI turbojet engines power the airplane.

Logbooks showed that an annual inspection of the airplane was completed on March 1, 2001. The logbook entry for that annual inspection revealed that the airplane accumulated 8,691 hours of total time. The logbook showed that the right engine, serial number 10060, had accumulated 1,848 hours since overhaul and the left engine, serial number 10112, had accumulated 1,525 hours since overhaul.

The airplane can be fitted with wing tip fuel tanks. The CM 170's manual listed two wing tip fuel tank types, a metal 122-liter tank and a polyester resin 230-liter tank. The manual stated that "a hollow shaft joints the front section of ribs 1 and 2. This fitting is threaded on the inside, to receive the front attachment of the tank. ... On aircraft below [number] 200, the rear attachment of the tank is bolted to a reinforcement plate carried by rib 1. As of aircraft [number] 200, the rear attachment of the tank, which has been lengthened, engages in the spool which links ribs 1 and 1A. It is bolted to rib 1A."

The airplane's special airworthiness certificate showed the airplane was certified in the experimental category for the purpose of exhibition. The airplane's experimental operating limitations listed the pilot as the registered owner. The special airworthiness certificate and the limitations and were dated January 9, 1998. An excerpt from the limitations stated:

7. No person may operate this aircraft for carrying persons or

property for compensation or hire.

8. No person may be carried in this aircraft during the exhibition

of the aircraft's flight capabilities, performances, or unusual

characteristics at air shows, motion picture, television, or similar

productions, unless essential for the purpose of the flight. Passengers

may be carried during flights to and from any event outlined in the

program letter or during proficiency flying, limited to the design

seating capacity of the aircraft.

...

10. The person operating this aircraft shall advise each person

carried of the experimental nature of this aircraft.

METEOROLOGICAL INFORMATION

At 0953, the LSE weather was: Wind variable at 3 knots; visibility 10 statute miles; sky condition clear; temperature 21 degrees C; dew point 12 degrees C; altimeter 30.04 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

An on-scene investigation was conducted. The fuselage and right wing were found 817 feet from the departure end of runway 21. The fuselage and right wing were found with a soot like substance on them. The fuselage was found deformed and consumed by fire. The grass in the area around the fuselage was found charred. The empennage forward of the v-tail was found deformed and covered with a soot like substance. Flight control push-pull link-rods were traced and continuity was established from the cockpits to the flight control surfaces. The left wing was separated from the fuselage and was located about 30 feet east of runway 21 at runway 21's intersection with runway 18. Sections of the v-tail were found on runway 21 where runway 21 and runway 18 intersect. Examination of the left wing and v-tail did not reveal any soot like discoloration. The left engine exhibited reverse bending of its compressor blades. The right engine exhibited scoring on its case along the plane of the turbine rotors. The airplane's wing tip tanks were found in the grass area between the end of runway 21 and the area where the fuselage came to rest. Both wing tip tanks had separated from their wings. The tanks were constructed of a fiberglass like material. See appended photographs and wreckage diagram.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy was performed on the pilot by the Minnesota Regional Coroner's Office on June 18, 2001.

The FAA Civil Aeromedical Institute prepared a Final Forensic Toxicology Accident Report. The report was negative for all the tests conducted.

TESTS AND RESEARCH

The left and right wing tip tank forward and rear attachment assemblies were forwarded to the National Transportation Safety Board's Materials Laboratory for examination. The laboratory produced Materials Laboratory Factual Report 01-112. See appended report. Excerpts from the report stated:

FORWARD ATTACHMENT ASSEMBLIES

The left tip tank forward assembly was fractured ... Examination

of the fracture in the left tank assembly ... revealed that the fracture

was copper colored, typical of a brass or bronze component, and that

the fracture was rough in texture, indicative of an overstress fracture.

No evidence of progressive cracking was noted on the fracture.

REAR ATTACHMENT ASSEMBLIES

The rear attachment assemblies consist of (1) a stud that attaches

to and protrudes from the fiberglass tank surface, (2) a "U" shaped

clevis that is threaded onto the stud and locked into position with a

jam nut, and (3) a quick release pin through the two tines of the

clevis. Both of the studs were fractured flush with the exterior

surfaces of the tip tanks.

Examination of the fractures through the studs revealed similar

features on the fractures from both tip tanks ... Both fractures

contained two diametrically opposite regions that were lighter in

color and contained crack arrest positions, typical of reverse

bending fatigue. On both studs fatigue initiation was from multiple

initiation sites within a thread root. ... The fatigue cracking on the

studs propagated through roughly 50 percent of the stud cross

section before final fracture. The fracture surface of the stud from

the right tank ... contained superficial rust-colored deposits over

the central portion of the fracture. The total lack of dark

discoloration on any portion of the fatigue regions indicates that

the fatigue crack areas were not exposed to the environment for a

significant time, and the relatively rough texture of the fracture

surface within the fatigue regions indicates rapid propagation of

the cracking.

Examination of the fracture faces of the stud pieces embedded

within the tank structure revealed that the fatigue regions were

on the upper and lower edges of the stud, based on the assumption

that the slight curvature of the tank piece was predominantly in the

hoop (circumferential) direction. Because the orientation of the

tank pieces was not provided, it was not determined whether the

upper or lower side of the studs contained the tensile side of the

bending deformation (the side with elongated threads).

The French aircraft accident investigation authority, the Bureau Enquetes-Accidents was contacted and asked to search their accident and incident records for occurrences of tip tank, tail, and wing separations. Three tip tank incidents were found. They occurred between 1980 and 1994. The aft mount was found broken in all these incidents. The Bureau did report that "Aerobatic evolutions were forbidden in the [French Air Force] for aircraft with 230 [liter] tip tanks. The Bureau further reported that there are "no French registered Fouga aircraft equipped with larger capacity tanks (230 [liter])."

ADDITIONAL INFORMATION

A FAA Inspector interviewed a witness. That record of interview stated:

There are multiple levels of sponsorship and her level invited

her to three rides - 1 in the T-6, 1 in the Golden Knights Aircraft

and 1 in the Fouga. She had taken the ride in the T-6 on Friday [June 15].

The coroner's report stated that the accident pilot "was hired by the family and friends of [the passenger] ... to take her for a ride in a jet as a wedding present."

The parties to the investigation included the FAA and the aircraft's crew chief. The Bureau Enquetes-Accidents assigned an Accredited Representative to assist in the investigation.

The aircraft wreckage and retained items were released to a representative of the insurance company.

NTSB Probable Cause

The fatigue failure of the aircraft's left wing tip fuel tank rear attachment, while the aircraft was being maneuvered in a low approach, leading to the tank's in-flight separation and subsequent in-flight break up of the airplane and the aircraft's control not possible.