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N711HZ accident description

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Tail numberN711HZ
Accident dateSeptember 17, 2000
Aircraft typeBeech S35
LocationLongmont, CO
Additional details: None

NTSB description

HISTORY OF FLIGHT

On September 17, 2000, at 1151 mountain daylight time, a Beech S35, N711HZ, registered to and operated by Hotel Zulu, LLC, was destroyed when it impacted terrain during an uncontrolled descent at Longmont, Colorado. The two airline transport certificated pilots were fatally injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the personal flight being conducted under Title 14 CFR Part 91. The flight originated at Boulder, Colorado, approximately 1020, with an en route stop at Erie, Colorado.

N711HZ was later identified, by radar coverage from the Denver Air Route Traffic Control Center (ARTCC) in Longmont, Colorado, to have departed to the south from Erie Tri-County Airport, Erie, Colorado. The National Track and Analysis Program (NTAP), provided limited information pertaining to aircraft headings, approximate times, and approximate airspeeds. No altitude information was recorded. The NTAP revealed that at 1144, N711HZ flew south from Erie Tri-County Airport until 1146, when it turned to the right and headed northwest at 306 degrees. At 1148, N711HZ turned to the right again and headed north at 359 degrees until its last primary radar return at 1151. During the time from 1144 to 1151, N711HZ's average speed was 100 knots, with a maximum speed of 135 knots at 1147 and a minimum speed of 75 knots at 1150.

Three witnesses saw the airplane just prior to the actual impact. The witnesses were personally interviewed and each submitted written statements. The first witness, who was standing outside her front door west of Highway 287 and the accident site, wrote: "I [saw] a plane just north of my home headed eastward. It seemed not to be running at full power but not flying particularly low or performing any stunt maneuvers, as we are accustomed to in this geographical area. It continued eastward and veered slightly to the north, attempting a full throttle climb and appeared (from my visual perception) to flip into about a 180-degree bank, and perhaps may have been upside down...but due to the position of the sun I could not say for certain. Immediately after this action, the craft nosed straight downward narrowly missing a farmhouse and a number of out buildings. Upon impact there was an incredible explosion and an immediate fire following thereafter lasting only a couple of minutes. A huge cloud of black smoke continued to be visible thereafter for some time."

The second witness was driving south on Highway 287 when he noticed "an airplane flying at approximately 50-100 feet in the air. The plane was headed east and I would estimate it to be 500 yards east of Highway 287. The plane showed no apparent signs of trouble, other than flying so low. The plane suddenly made a sharp right turn to the south and turned upside down. The plane then nose-dived into the ground and exploded on impact."

The third witness was riding his bicycle on a dirt road paralleling an irrigation ditch just east of the accident site. He wrote, "...I was startled by the sound of an aircraft engine/prop which had suddenly increased in pitch and loudness. I looked up and saw a small airplane almost completely over on its back. The wings were almost parallel to the ground with the right wing of the airplane slightly higher than the left. I estimate the angle of the wings from horizontal to be 10 to 20 degrees. My direction of travel was towards the west, and the nose of the aircraft was pointed away from me in a northwesterly direction. From my position the aircraft appeared to be between 45 and 60 degrees from vertical and slightly north of me. The nose of the aircraft was initially pitching over. When it was pointed at the ground the aircraft stopped pitching and went into an almost vertical dive. The aircraft was oriented with the top of the airplane in a southeasterly direction. It appeared to be moving slowly when the dive started, maybe 20 to 30 mph... While it was pitching over I noticed the distinctive V-tail. After the airplane entered the dive, it did not change the direction of its forward motion until it was about 50 feet above the ground. At that time it appeared to start pulling out of the dive. However, the airplane was so close to the ground there was only a small change in its direction before it struck the ground...From the time I first saw the aircraft until it struck the ground there was no smoke or flames visible and the engine was running. The airplane appeared to be completely intact. The entire sequence of events took about 5 seconds..."

Occupants of two nearby houses said they heard a loud noise that shook their houses, and then heard an explosion. They then observed a fireball in the field. Other witnesses reported hearing the airplane pass overhead. One witness, a United Air Lines pilot who did not see the impact, reported hearing the engine make an unusual "popping" sound. Shortly thereafter, he saw smoke and drove to the scene. Another witness, standing in a field adjacent to the accident site, saw the airplane flying slow from south to north about 150 feet above the ground. Engine sounds stopped and the airplane disappeared from view behind a barn. He, too, heard the impact and saw smoke, and ran to the scene.

The accident occurred during the hours of daylight at a location of 40 degrees, 7.685' north latitude, and 105 degrees, 5.611' west longitude.

PERSONNEL INFORMATION

The left seat pilot held an airline transport pilot certificate, dated September 14, 1994, with an airplane multiengine land rating, type ratings in the Boeing 727, Boeing 757/767, and Learjet, and commercial privileges in airplanes single engine land. He also held a flight engineer certificate, dated December 5, 1969, with a turbojet rating. He also held a first class airman medical certificate, dated September 10, 1998, with no restrictions or limitations. At the time he made application for this medical certificate, he estimated he had accrued 18,200 total flight hours, 400 hours of which were accrued in the previous six months (see exhibits for more details of flight time). He was a retired American Airlines captain.

The right seat pilot held an airline transport pilot certificate, dated July 18, 1996, with an airplane multiengine rating, type ratings in the Boeing 737, Douglas DC-9, and Learjet, and commercial privileges in airplanes single engine land. He held a flight engineer certificate, dated May 5, 1972, with turbojet and turboprop ratings, and a flight instructor certificate, dated October 21, 1977, with an airplane single engine rating. He also held a first class airman medical certificate, dated May 1, 2000, with the restriction, "Must have available glasses for near vision." At the time he made application for this medical certificate, he estimated he had accrued 18,000 total flight hours, 700 hours of which were accrued in the previous six months (see exhibits for more details of flight time). He had been an Eastern Air Lines and a United Air Lines captain. After his 60th birthday, he continued to fly as a flight engineer with United Airlines, a position he held at the time of the accident.

The two pilots were brothers. The left seat pilot had 50.19 hours in the Beech S35. According to a Hotel Zulu, LLC, spokesman, the right seat pilot had never flown the airplane.

AIRCRAFT INFORMATION

N911HZ (s/n D-7699), a model S35, was manufactured by the Beech Aircraft Corporation in December 1964. It was equipped with a Teledyne Continental IO-520-BA(3) fuel injected engine (s/n 280688-R), rated at 285 horsepower, and a McCauley 2-blade, all metal, constant speed propeller (m/n 2A36C23-PCE).

According to the airplane maintenance records, the last annual inspection was performed on July 14, 2000, at a tachometer time of 1,422.36 hours and a total airframe time of 3,651.37 hours. The engine was factory rebuilt by Teledyne Continental Motors on February 28, 1991, and was installed on N911HZ on March 20, 1991. At the time of the annual inspection, it had accumulated 786.64 hours. The propeller was overhauled on January 25, 1990, and installed in N911HZ on July 7, 1990. At the time of the annual inspection, it had accumulated 837 hours since overhaul.

METEOROLOGICAL INFORMATION

Weather observed at Jefferson County Airport, Broomfield, Colorado, located 18 n.m. south of the accident site, was as follows:

1753Z (1153 mst): Wind, 170 degrees at 4 knots; visibility, 25 s.m.; scattered clouds, 11,000 feet; broken clouds, 20,000 feet; temperature, 32 degrees C. (90 degrees F.); dew point, 4 degrees C. (39 degrees F.); altimeter setting, 30.13 inches of mercury; remarks, smoke west over foothills.

WRECKAGE AND IMPACT INFORMATION

The on-scene examination commenced and terminated on September 17, 2000. The airplane came to rest on a magnetic heading of 122 degrees, and the engine was aligned on a magnetic heading of 140 degrees. The engine crater was about 24 inches deep. The engine's angle of impact into the ground was approximately 60 degrees nose down with the rear of the engine about 18 degrees to the left (as viewed from the rear) of vertical. Other than the engine crater and wing impact marks, there were no other ground scars.

The cockpit and cabin area had sustained extensive thermal damage. The throttle, mixture, and propeller controls were full forward. The landing gear bellcrank was retracted and the flap jackscrews were extended 6 inches. According to Raytheon Aircraft Company, these settings are equivalent to the landing gear up and the flaps being fully deployed. The ruddervator trim measured 1/2 inch, or 5 degrees tab down. Control continuity was established from all flight control surfaces to a point beneath the seats. Thermal damage precluded further continuity checks. The fuel selector valve was positioned on the left main tank; the broken handle was pointing to the right main tank. The fuel screen was clear of debris.

Postimpact fire consumed most of the inboard portion of the left wing. The left wing was separated at wing station (W.S.) 115 and displaced aft almost perpendicular to the normal orientation of the wing. The wing tip had also separated outboard of the aileron and was found next to the left engine cowling.

One propeller blade was visible (blade 1), the other blade (blade 2) was beneath the engine. The propeller assembly was extricated from the engine crater. There was "S' bending on both blades and twisting towards low pitch. There were chordwise scratches on the cambered surfaces. The crankshaft separated in torsion and bending overload.

MEDICAL AND PATHOLOGICAL INFORMATION

Autopsies (00A 122 and 00A 123) were performed on both pilots by the Boulder County Coroner's Office, and toxicology screens (#200000270002 and #200000270001) were performed by FAA's Civil Aeromedical Institute. The left seat pilot tested negative for carbon monoxide, cyanide, ethanol, and drugs. The right seat pilot tested negative for carbon monoxide and drugs, but 0.74 (ug/ml) cyanide, 11 (mg/dL, mg/hg) ethanol and 2 (mg/dL, mg/hg) acetaldehyde were detected in blood. According to CAMI's report, the ethanol detected may have been the result of postmortem ethanol formation.

TESTS AND RESEARCH

The engine was disassembled and examined at Beegles Aircraft Services in Greeley, Colorado, on September 27, 2000. The engine driven fuel pump drive shaft (p/n 653359A) was found fractured at the shear point. The drive shaft was submitted to NTSB's metallurgical laboratory for examination. According to the materials laboratory factual report, "The fracture surface had a rough appearance typical of overstress failure. A lip was observed on one fracture surface...a feature typical of the location of final fracture in bending. No rotational damage was observed on the fracture face that would be indicative of an in-flight fracture, and no evidence of a preexisting crack was observed." No other discrepancies were noted during the engine disassembly.

The throwover control wheel was examined and was determined to have been in the right position at the time of the accident. The holes in the control column and bracket were aligned, and an impact compression wrinkle in the control column prevented post accident disturbance. Examination of the chain-sprocket assembly through the access hole in the rear of the control column was consistent with the control column being in the right seat position.

ADDITIONAL INFORMATION

According to pilots familiar with the S35 Bonanza, it has conventional flight and stall characteristics in uncoordinated flight or in a cross-controlled stall. Chapter 5-2 of FAA's "Airplane Flying Handbook" (FAA-H-8033-3) states: "In a cross-control stall, the airplane often stalls with little warning. The nose may pitch down, the inside wing may suddenly drop, and the airplane may continue to roll to an inverted position. This is usually the beginning of a spin. It is obvious that close to the ground is no place to allow this to happen. Recovery must be made before the airplane enters an abnormal attitude (vertical spiral or spin); it is a simple matter to return to straight-and-level flight by coordinated use of the controls. The pilot must be able to recognize when this stall is imminent and must take immediate action to prevent a completely stalled condition. It is imperative that this type of stall not occur during an actual approach to a landing, since recovery may be impossible prior to ground contact due to the low altitude."

In addition to the Federal Aviation Administration, parties to the investigation included the Raytheon Aircraft Corporation and Teledyne Continental Motors.

The wreckage was released to the insurance company on February 1, 2001.

(c) 2009-2011 Lee C. Baker. For informational purposes only.