N94U – Beechcraft (Textron Aviation) F90 – 2000-11-24 NTSB Accident Report

HISTORY OF FLIGHT

On November 24, 2000, at 1151 eastern standard time, a Beech King Air F90, N94U, was destroyed during a forced landing after takeoff from the Lynchburg Regional Airport (LYH), Lynchburg, Virginia. The airplane was consumed by a post-crash fire. The certificated commercial pilot and the certificated pilot-rated mechanic were not injured. Visual meteorological conditions prevailed for the flight that originated at Lynchburg, about 1150. No flight plan was filed for the post-maintenance test flight, conducted under 14 CFR Part 91.

According to the pilot, the test flight followed the installation of an overhauled engine on the right side of the airplane. Prior to the flight, all ground checks were satisfactory, and the only discrepancy noted was that, at idle, the right propeller indicated 90-100 rpm higher than the left propeller.

The airplane was subsequently released for flight, and the pilot determined that the rotation speed (Vr) was 97 knots. Prior to takeoff, he completed the engine-start and before-takeoff checklists with no anomalies noted. According to the pilot:

"We finished the pre-takeoff checklist - and centerline checks - and everything was nominal, all the way through Vr. Vr was Vmc plus 10 knots, about 95 knots. The call before Vr was 'Everything was normal, no master cautions, no segments.' We rotated and came off the ground very normally. We rotated at the normal point on the runway, about 1,500 or 1,600 feet down. We were at the right speed and the right distance at takeoff.

We showed a positive rate of climb and I reached for the gear handle. I couldn't get it up because it was on that lousy down latch. At that point we were 100 feet off the ground and I sensed a loss of thrust. I pitched to the blue line, but we weren't climbing. I looked at the gauges and everything was normal but we were not climbing."

The pilot determined that the airplane would not fly, and selected a forced landing area to the left and just beyond the departure end of the runway. He completed the forced landing, and both occupants egressed the airplane without injury.

The pilot was asked to describe the engine instrument readings during the takeoff and after he perceived the apparent loss of thrust. According to the pilot:

"I looked at temperature and prop - everything was matched. The aircraft came off with no yaw and I pitched down to blue line. I reached to select the landing gear up and the landing gear would not come up. My conclusion was that the safety latch was holding it down. When I felt the loss of power, I felt no particular yaw because of the autofeather and the rudder boost.

The temperature and torque indicated I had power, but I clearly was not climbing. Both appeared normal and I did not see a split in values. I did not see N1, I just don't remember. I was sure I had a catastrophic failure, but I couldn't verify which side. We were not gaining altitude, we were bleeding airspeed, and I tried three times to get the gear up."

When asked if he heard the stall warning horn, the pilot said that he had, and that he then lowered the nose of the airplane. As soon as he lowered the nose, the horn went away.

The mechanic also reported that the inspections and ground runs were completed with only the 100-rpm difference in the idle speeds between the two engines. When interviewed, the mechanic said:

"We started the aircraft and taxied down to the runway. We went through the checklists, checked the props, and were waiting on the tower. We took the runway and I visually verified we had 800 pounds of fuel per side.

[The pilot] pushed the power levers forward and all the needles matched and looked okay. I watched the airspeed and Vr was about 95 to 100 knots. We came off the runway very quickly in under 2,000 feet. Everything seemed normal.

[The pilot] reached to select gear up, and something didn't feel right. He said, 'We've got a problem'. I knew something was wrong but I couldn't put my finger on it.

We were not climbing. We were too low, too slow, and we were not going to make it back. I just felt that we were not climbing like we should. I don't remember any engine noises like the engine spooling down. Just this feeling that we were sinking in."

In a written statement, the mechanic said:

"The engine start-ups were normal. We requested and received clearance to taxi to runway 4. While taxiing to runway 4 [the pilot] engaged the reverse mode and then brought the controls back out of 'reverse'. Also during taxi the entire checklist was read by me to [the pilot], with [the pilot] verbally responding as he accomplished each item that had been read. Upon reaching the approach end of runway 4, [the pilot] called the tower again and stated that we were ready to depart, with the tower clearing us for takeoff. While taking the active runway I looked at the fuel quantity gauges verifying that we had 800 lbs. of fuel per side.

Upon taxiing into position [the pilot] applied power and I visually verified both torque's and RPM were both coming up evenly and together. The takeoff roll was normal in all aspects with rotation occurring between 95 and 100 knots and well within the first 2000 feet of the runway. Our climb out was normal with no annunciator lights appearing and no abnormal engine sounds. Upon reaching approximately 200 to 300 feet off of the ground, [the pilot] selected the "gear up" position, after which I recall him stating, "We have a problem." At about that same time I felt that something was wrong with the aircraft. It felt as if we were slowing down (airspeed) and I could definitely tell that we were not climbing, as we should. (At no time did I feel a yaw in any direction, although at or around the time that [the pilot] selected "gear up" a slight left roll was noticed, but immediately corrected for.)"

In a written statement, one witness said he was watching aircraft arrive and depart the Lynchburg airport and that he was monitoring the tower frequency on a hand-held transceiver. He said:

"At the time of the incident I witnessed the King Air lift off from the runway. While I admittedly know very little about turbine-powered aircraft it seemed apparent right away that the pilot was experiencing a problem. The plane seemed like it was not accelerating and it was not gaining altitude.

The sound from the engines seemed louder than what I have heard before while watching other King Airs lift off. The gear was still down and the wings started rocking back and forth about 10 to 15 degrees. Shortly after lift-off I heard the pilot call the tower and declare an emergency. Shortly after the pilot declared, I lost site of the plane just past the end of the runway. A few seconds later I saw a large column of smoke and immediately drove my car to the crash site... [The pilot] stated that he didn't know what happened but thought the engines might have been 'over-torqued'."

The accident occurred during the hours of daylight at 37 degrees, 20 minutes north latitude, and 079 degrees, 12 minutes west longitude.

PERSONNEL INFORMATION

The pilot held an airline transport pilot certificate with ratings for airplane single engine land, multiengine land, and instrument airplane. He held a flight instructor certificate with ratings for airplane single engine land, multi-engine land, and instrument airplane.

The pilot's most recent Federal Aviation Administration (FAA) second-class medical certificate was issued February 2, 2000. The pilot reported 12,000 hours of total flight experience, 5,000 hours of multi-engine experience, and 250 hours of experience in make and model.

AIRCRAFT INFORMATION

The airplane was a 1981 Beechcraft Model F90 King Air, with 6,788 aircraft hours. Two Pratt and Whitney PT6 gas turbine engines powered the airplane. The engines drove two Hartzell constant-speed controllable-pitch propeller assemblies. The airplane was on an Approved Aircraft Inspection Program (AAIP). The most recent AAIP inspection was performed on August 3, 2000, at 6,773 aircraft hours.

The installation of the right engine began November 18, 2000. The final rigging adjustment was made November 24, 2000, on the morning of the accident.

Four mechanics and the director of maintenance were involved in the installation of the right engine, and the subsequent rigging of both engines. Each mechanic held an FAA mechanic certificate, with ratings for airframe and powerplant. The director of maintenance was also a certificated mechanic, with inspection authority.

There was no lead mechanic assigned to the job, and the mechanics working on the airplane would change from day to day. However, one mechanic was consistently involved with the operation, and was involved in the rigging of both engines during the last 3 days of work. This first mechanic provided a written statement with a chronological description of events.

The first mechanic also stated that he had considerable experience rigging Garrett-powered airplanes, but little experience with Pratt and Whitney-powered airplanes, and no experience with this particular propeller system. He said he had no formal training on the Beech King Air.

Interviews with the other three mechanics revealed that none of them had formal King Air training either.

Examination of maintenance records revealed that the installation and rigging of the right engine, and the rigging adjustments of the left engine, were not documented. Run-up graphs, required by the maintenance manual to determine target torque values and engine performance, were not completed.

The first three paragraphs of the first mechanic's statement described the engine installation itself with a second mechanic, and subsequent paragraphs discussed the rigging with a third and fourth mechanic. According to the first mechanic:

"On November 22, 2000, [the third mechanic] and I started to check the engine rigging and adjusted the power lever cam. We also adjusted the beta valve flush. The engine run was performed; [the third mechanic] and I noticed a torque split and the low idle needed to be increased. About this time, [the third mechanic] left work. I began to adjust the low idle speed first. I then began to adjust the low idle torque on the right engine. I performed another engine run and torque was a little high on the right and noticed the left engine was low. I adjusted the left engine torque about one-quarter turn on the barrel nut, and then adjusted the right engine down. At this time, I also adjusted the fuel control unit one turn in. I ran the aircraft again, the low idle torque was matched and flight idle torque checked good. At the close of the day, [the maintenance director] inspected the engine rigging; all that was left at this time was safetying all controls and adjusting the prop lever on the right hand engine.

On November 24, 2001, [the fourth mechanic] and I began to safety wire engine controls on R/H engine. [The fourth mechanic] began to inspect the complete engine on the right hand side and the left engine where I adjusted the torque. I adjusted the rod end on the propeller control linkage to adjust the lever. We both cowled the right hand engine. We later ran the aircraft and checked the engine parameters on both engines and checked all engine functions. The engines were to our satisfaction with the exception of a 100-rpm split of the prop speed. After the engine runs I began to do some paperwork for a test flight while [the fourth mechanic] performed a walk around of the aircraft and notified [the pilot] that the aircraft was ready for a test flight."

During an interview, the first mechanic said:

"We did the majority of the engine runs on the twenty-second [of November]. Four or five runs were done with [the third mechanic], and then I did two myself. Two runs were to get the idle speed. I adjusted the left engine a hair. It didn't really have a run sheet. I noticed a torque split, about 80 pounds, so I adjusted the left engine. One easy adjustment on the left side got rid of it."

When asked if he verified the pressure altitude and torque parameters, and first mechanic said, "No, I didn't. I just did a good run."

He further stated that there were no installation or rigging instructions with the engine when it was delivered from the maintenance facility, and that the mechanics used a Beech maintenance manual dated December 1995. He also stated that he had spoken to a Raytheon Aircraft Corporation (Beech) representative early in the project, but not at the time that the rigging was performed.

During a group discussion of the rigging procedure with the first mechanic, a representative of the Raytheon Aircraft Corporation, and an FAA airworthiness inspector, it was revealed that the first mechanic misinterpreted guidance provided for the use of Pressure Altitude and Temperature Conversion Graphs in the maintenance manual. The proper graph for setting ground idle torques in this application was Graph 4. However, the first mechanic's interpretation of the text lead him to use Graph 5.

Interpolation of Graph 5 resulted in ground idle torque values higher than those called for in Graph 4 under the same atmospheric conditions. Subsequent to rigging the right engine to the torque values called for in Graph 5, the mechanics adjusted the rigging of the left engine to match that of the improperly-rigged right engine.

The mechanic said that he performed a ground idle torque check, but did not perform a flight idle torque check.

METEOROLOGICAL INFORMATION

The weather reported at the Lynchburg Regional Airport included calm winds and clear skies.

AERODROME INFORMATION

The Lynchburg Regional Airport was tower-controlled, with two runways that intersected at the north end of the airfield. Runway 03/21 was 5,799 feet long and 150 feet wide. Runway 35/17 was 3,987 feet long and 150 feet wide. The field elevation was 938 feet.

WRECKAGE AND IMPACT INFORMATION

The wreckage was examined at the site on November 25, 2000, and all major components were accounted for at the scene. The wreckage was located in a rough, hilly area just beyond the airport perimeter road and fence that was recently cleared of standing timber.

The airplane came to rest upright, and the left wing, cockpit, and cabin areas were consumed by post-crash fire. The main gear was collapsed, the nose gear was separated, and the engines were displaced in the nacelles.

The wreckage path measured 190 feet from the initial ground scar to the main wreckage, and was oriented 010 degrees magnetic. The airplane faced approximately opposite the direction of travel and was oriented 240 degrees magnetic. The wreckage path was divided into 1-foot increments called wreckage points (WP).

A curved, elliptical trench, approximately 6 feet long, 1 foot wide, and 8 inches deep was located at WP 30. An angular cut log approximately 4 inches in diameter was buried beneath the ground, but exposed at the leading edge of the trench. Several angular-cut and 'broom-strawed' saplings were found along the wreckage path prior to the trench.

The left propeller, propeller gearbox, and the power section of the left engine were located at WP 123, 15 feet left of centerline. Examination of the left engine revealed severe rotational scoring of the compressor turbine and the interstage baffle upstream side. Lighter rotational scoring was noted on the power turbine disc and the interstage baffle downstream side. The turbine blades were cracked, broken, and bent opposite the direction of rotation.

The main wreckage came to rest at WP 190, with the gas generator section of the left engine still in the nacelle. The right engine was attached to the airframe in the right engine nacelle. The engine was impact- and fire-damaged. The propeller hub was attached to the engine and all four propeller blades were in the hub.

TESTS AND RESEARCH

The left and right propeller assemblies, and both engines were examined at the scene on November 27 and 28, 2000, under the supervision of an FAA aviation safety inspector.

Examination of the left propeller assembly revealed broken pitch change links on the #1 and #3 blades. Pitch change linkage on the #2 and #4 blades were intact. The spinner dome was pressed over the propeller blades, with impression marks from the #1, #2, and #4 blade counterweights at the feather position.

Examination of the left propeller blades (all four) revealed forward bending, with no twisting. All four blades exhibited rotational scoring. The #1, and #2 blades displayed some chordwise scratching and trailing edge gouging.

Examination of the right propeller blades (all four) revealed forward bending, with no twisting. All four blades exhibited rotational scoring. The #2 and #3 blades displayed leading edge gouging near the tips. The pitch change mechanism was broken on blade #3, but was intact on the other three blades. The spinner dome was pressed over the propeller blades, with impression marks from the #4 counterweight at the feather position.

Examination of the right engine revealed severe rotational scoring on the compressor turbine and the interstage baffle on the upstream side. Lighter rotational scoring was also noted on the power turbine disc and the interstage baffle on the downstream side. The baffle's downstream face also displayed concurrent static imprint marks.

ADDITIONAL INFORMATION

A landing gear squat switch was used to activate a solenoid connected to the propeller-reversing lever. The lever was connected to the propeller governor beta valve. The purpose of the solenoid was to move the beta valve from the ground idle position to the flight idle position at takeoff, when weight was removed from the landing gear. Continued movement of the beta valve in this direction restricted or stopped oil flow to the propeller dome. The restriction or absence of oil pressure to the dome, allowed movement of the propeller blades towards the feather position.

Specific ground idle torque checks and flight idle torque checks were prescribed in the maintenance manual whenever rigging or adjustments were performed on components within this system.

Activation of the Ground Idle Stop Test Switch in the cockpit simulated the weight removed from the landing gear, as in a takeoff, and the solenoid moved the beta valve from the ground idle position toward the flight idle position. The flight idle torque check required the Ground Idle Stop Test Switch be pressed and held, the power levers advanced, the engine RPM stabilized, and the propeller torques read and verified.

The pilot was required to perform a Ground Idle Low Pitch Stop check during the Before Takeoff Run Up check. However, the check only required the pilot to depress the Ground Idle Stop Test Switch, note a decrease in propeller rpm, and release the switch. The pilot was not required to wait for the propeller rpm to stabilize in the flight idle position with the switch depressed.

At no time during either the maintenance test-runs, or the pilot's before takeoff engine run, was the Ground Idle Stop Test Switch held, and the beta valve allowed to move and stabilize at it's adjusted flight idle torque position.

In-flight circumstances similar to those described in this report were also described in the following accident reports:

FTW91FA029, Beech F-90, Nagadoches, Texas, November 11, 1991

CHI97FA256, Beech 65-A90, Alice, Texas, August 12, 1997

An FAA maintenance alert published in 1996 described an incident at the Hartzell Propeller Service Center that involved a Beech A-100. According to the Alert:

"On the first flight after propeller installation, both propellers had a dramatic RPM loss immediately after lift off from the runway, fortunately the aircraft was able to land safely. This aircraft, and certain other Beech [Pratt and Whitney] powered aircraft, have a two position low blade angle which effectively provides both a flight idle and a ground idle stop, the difference controlled by a landing gear switch. The combination of switch actuation plus an engine/propeller combination that was not properly rigged, initiated the incident."

As a result of this investigation, the Raytheon Aircraft Company published changes to the Beech F90 Maintenance Manual dated July 18, 2001, regarding idle adjustments, ground idle torque checks, and flight idle torque checks. The changes included improved text, larger diagrams, and a warning which stated:

"Make certain the forward edge of the conical cap nut is between the two chamfer faces of the beta valve and no part of the beta valve piston is visible outside the cap nut. Misadjustment of the beta valve can cause unplanned propeller feathering, resulting in a possible hazard to airplane operation and over torque damage to the engine."

Raytheon Aircraft Company also published changes to the Beech King Air F90 Pilot's Operating Handbook in the Normal Procedures Section IV, dated June 2001. The changes to the Ground Idle Low Pitch Stops check were as follows:

a. Condition Levers - HIGH IDLE

b. Power Levers - IDLE (note propeller rpm)

c. Prop Test Switch - HOLD TO GROUND IDLE STOP

d. Prop RPM - STABILIZED APPROX. 200 RPM BELOW VALUE IN STEP b.

e. Prop Test Switch - RELEASE

f. Prop RPM - VERIFY RETURNS TO VALUE IN STEP b.

g. Condition Levers - Low Idle

The airplane wreckage was released on December 5, 2000, to the president of Virginia Aviation.