[NTSB AAR-04/01, ¶1.5
- The captain, age 25, was hired by Air Midwest in March 2000. She held an airline transport pilot certificate and a Federal Aviation Administration (FAA) first-class medical certificate dated November 19, 2002, with no limitations. The captain received a type rating on the Beech 1900D in March 2001. [ . . . ] The captain received her private pilot certificate in February 1997.
- In post accident interviews, Air Midwest pilots who had flown with the captain made favorable comments about her piloting skills. A check airman stated that the captain had no difficulties during upgrade training and that she demonstrated very good knowledge of the airplane's systems and very good judgment. Another check airman described the captain as one of the better company pilots and stated that she made very good decisions about flying. First officers stated that the captain was a thorough and methodical pilot who controlled the airplane well and involved them with the flight by asking for opinions and letting them review paperwork.
The captain went from private pilot to airline pilot in just five years and had been flying for just six years on the date of this crash. All indications were that she was a very good pilot and that she showed up for flight well rested..
- In post accident interviews, Air Midwest pilots who had flown with the first officer made favorable comments about his piloting skills. Pilots described the first officer as a talented and very precise pilot with good attention to detail and good communication skills. Pilots also stated that the first officer possessed good situational awareness and good knowledge of the Beech 1900D.
- The quality assurance inspector, age 50, was hired by RALLC in July 2002. He was initially hired as a mechanic at the HTS maintenance station and was subsequently promoted to foreman and secondary (backup) quality assurance inspector. [ . . . ] The primary quality assurance inspector was not at work on the night of January 6, 2003, so the foreman/secondary quality assurance inspector assumed his duties.
- The quality assurance inspector stated that he was providing OJT to two mechanics and that it was his first time training two mechanics while performing inspector duties.
- At the public hearing for this accident, the quality assurance inspector testified that he had performed elevator control system rigging work once.
The Pitch Control System
Figure: Beech 1900D pitch control system, from NTSB AAR-04/01, figure 4.
Click photo for a larger image
[NTSB AAR-04/01, ¶1.6
- The Beech 1900D airplane is equipped with a mechanically operated pitch control system. The three primary elements of the pitch control system are the elevators, the control column, and the connecting rods and cables. The elevators (left and right) are attached to the trailing edge of the horizontal stabilizer, which is mounted on top of the vertical stabilizer in a T-tail configuration. A pilot pushes forward on the control column to move the elevator trailing edges down (resulting in the airplane pitching AND) and pulls back on the control column to move the elevator trailing edges up (resulting in the airplane pitching ANU).
- The inboard end of each elevator has a control horn that is connected to the elevator surface by a shaft. Four primary stop bolts (left upper, left lower, right upper, and right lower) are mounted on airplane structure. The limit of travel for each of the elevator control horns is contact with an up stop bolt or a down stop bolt. The Beech 1900D AMM, section 27-30-02, indicates that the elevator primary stop deflection settings are 20° +1j/-0° up from the neutral position and 14° +1°/-0° down from the neutral position. The elevator's neutral position is the point at which the position of the trailing edge of the elevator is aligned with the chord plane of the horizontal stabilizer.
- Control cable assemblies (one ANU and one AND) connect the aft bellcrank to the forward bellcrank. The control cable assemblies have two cable sections joined by turnbuckle assemblies located in the base of the vertical stabilizer. Each control cable assembly comprises seven spirally wound strands and has one long and one short component. The turnbuckle assemblies establish the correct tension in the cables. Each turnbuckle assembly consists of a barrel and two threaded cable terminals.
- The accident airplane was equipped with a mechanically operated pitch trim control system. The pitch trim control system includes a single movable trim tab for each elevator and a cable-driven jackscrew actuator for each tab. The trim tabs, which are located on the inboard trailing edge of each elevator, relieve the force a pilot must hold on the control wheel to provide longitudinal control (for example, angle of attack or pitch) of the airplane. According to the Beech 1900D AMM, the trim tabs move from 5.75° ±0.25° up to 17° ±0.5° down. Movement of the trim tabs in the downward direction creates an upward aerodynamic moment on the elevator and results in an ANU pitching moment.
[NTSB AAR-04/01, ¶18.104.22.168] ELEVATOR CONTROL SYSTEM RIGGING
The procedure that follows includes several steps that are not applicable and some that were intentionally skipped.
Green on black items are not applicable to this airplane.
Black on amber items were applicable but intentionally skipped.
- Disconnect the autopilot servo cables.
- Locate and remove all access panels from the vertical and horizontal stabilizers to gain access to the aft elevator bellcrank and the elevator cables.
- Locate and remove the flight compartment seats, carpet, and floorboards to gain access to the forward elevator bellcrank.
It was possible to view a required rig pin without removing the first officer's seat but it was easier with the seat removed.
- Locate and remove the passenger seats, carpet, and floorboards on the right side of the passenger compartment to gain access to the elevator cable turnbuckles.
- Install an elevator travel board on each elevator at station 50.00.
A travel board is a calibrated template that attaches to the trailing edge of the horizontal stabilizer that allows a person positioned at eye level to see exactly how far up or down the elevator has moved. The text of the report's factual information does not note this step was skipped but the analysis and findings section imply that it was. It makes sense that it was, otherwise the mechanics would have detected the resulting limited elevator travel.
- Adjust the center-to-center length of the push-pull tube assembly between the control column and the forward elevator bellcrank to a dimension of 15.12 ± 0.06 inch.
- Adjust the surface stop bolts on the elevator control horn support for up-travel of 20° + 1° - 0 and down-travel of 14° + 1° - 0°.
- Verify the bob weight stop bolt clearance is 0.5 ± 0.06 inch. Adjust if necessary.
- Adjust the forward bellcrank stops for 0.37 ± 0.06 inch clearance from the stop bolts.
- Verify the forward bellcrank stop bolts make contact before the bob weight stop bolts make contact with the weight.
- Install a rig pin in the aft elevator bellcrank.
NOTE: Verify threads are visible through the inspection holes at the end of the pushrods after adjustments are made.
- Adjust the pushrods between the aft elevator bellcrank and the elevator to position the elevator at neutral (0° deflection).
- Remove the rig pin from the aft elevator bellcrank.
- Remove the safety clips from the turnbuckles and release cable tension.
- Move the control yoke to install the rig pin in the forward elevator bellcrank.
- Tighten the elevator-up cable until the elevator rises to neutral (0° on the travel board).
- Tighten the elevator-down cable until the average tension of the up- and down-cables is 66 ± 8 pounds (the sum of up-cable and down-cable tensions, divided by two). Refer to Figure 203.
- Continue to balance the adjustment of the two cables until the average tension is 66 ± 8 pounds while maintaining 0° deflection of the elevator.
- Perform the CONTROL COLUMN SUPPORT ROLLER INSPECTION procedure.
- Install safety clips on the turnbuckles.
- On aircraft equipped with the F1000 Flight Data Recorder, calibrate the Pitch Position Potentiometer. Perform the FLIGHT DATA RECORDER (FDR)̃ PITCH ADJUSTMENT procedure.
The mechanic thought this unnecessary and the quality assurance inspector thought the airplane didn't have an FDR.
- Remove the travel boards from the horizontal stabilizers.
See step e.
- Connect the autopilot servo cables to the elevator primary control cables.
- Install the seats, carpet and floorboards.
- Replace all access panels.
Step a, to disconnect the autopilot servo cables, and step w, to connect the autopilot servo cables to the elevator primary control cables, were not applicable to the accident airplane because it did not have an autopilot. Step d, to locate and remove the passenger seats, carpet, and floorboards on the right side of the passenger compartment to gain access to the turnbuckles, was not applicable because the elevator cable turnbuckles for the Beech 1900D model are not located under the passenger compartment floorboards.
[NTSB AAR-04/01, ¶22.214.171.124]
Photo: Turnbuckles as found in the wreckage, from NTSB AAR-04/01, figure 6.
Click photo for a larger image
[NTSB AAR-04/01, ¶1.12.4]
- The rivets connecting the elevator control horns to the elevator shafts were tight, and the control horns were solidly fixed to the elevator shafts. The control horns moved freely in their respective bearings. The primary stop bolts were attached to the elevator control horn supports and were found safety wired.
- The ANU turnbuckle was almost fully contracted, and the AND turnbuckle was almost fully extended. The measurement from the center of the tooling hole in one threaded cable terminal to the center of the tooling hole in the other cable terminal was 5.54 inches for the ANU turnbuckle and 7.30 inches for the AND turnbuckle. In addition, the AND turnbuckle had one thread visible, and the ANU turnbuckle did not have any threads visible. Figure 6 shows the turnbuckles as found in the wreckage and a drawing that shows a turnbuckle barrel and threaded cable terminals.
- The AND turnbuckle was extended 1.76 inches more than the ANU turnbuckle. After the accident, Air Midwest surveyed its entire fleet of 42 Beech 1900D airplanes, which represented 25 percent of the 164 Beech 1900D airplanes active in the North American fleet. Air Midwest data submitted to the Safety Board indicated that, on average, the AND turnbuckle was extended 0.04 inch less than the ANU turnbuckle.
- The elevator trim tab control wheel was intact and was attached in the cockpit. The pitch trim appeared to be near the full AND position. The pitch trim control cables were broken. The control cables were in the correct orientation. The left and right drums had their respective cables wrapped around to the middle position.
[NTSB AAR-04/01, ¶2.3]
- Flight data recorder (FDR) and CVR data from the accident flight showed that the airplane was rotating airplane nose up (ANU) after takeoff, even though the flight crew was pushing the control column fully forward and trimming the airplane in the airplane-nose-down (AND) direction. Neither of these actions allowed the flight crew to control the airplane's pitch attitude.
- FDR data, ground test results, and the airplane performance study for this accident showed that, before the accident airplane's detail six (D6) maintenance check on January 6, 2003, at Air Midwest's HTS maintenance station, the airplane's full range of downward elevator travel was available. FDR data, ground test results, and the airplane performance study also showed that, after the D6 maintenance check, the airplane's downward elevator travel was limited to about 7° rather than the 14° to 15° specified in the Beech 1900D Airliner Maintenance Manual (AMM).
- The mechanic determined that the accident airplane's cables needed to be adjusted because their average tension was too low. He stated that he adjusted the cables and performed some, but not all, of the steps of the elevator control system rigging procedure (section 27-30-02) in the Beech 1900D AMM. However, whenever cable tension adjustments are made, the entire elevator control system rigging procedure needs to be performed and not just those steps that apply to cable tensioning.
- Examination of the accident airplane's pitch control cable turnbuckles as found in the wreckage revealed that the AND turnbuckle, which measured 7.30 inches in length, was extended 1.76 inches more than the ANU turnbuckle, which measured 5.54 inches in length. However, according to data from Air Midwest's post accident survey of its entire fleet of 42 Beech 1900D airplanes, the AND turnbuckle was extended, on average, only 0.04 inch less than the ANU turnbuckle. Further, ground tests showed that turnbuckles adjusted to the lengths of those found in the wreckage would result in limited downward elevator travel, although the FDR would indicate that full downward travel was available.
- The Safety Board concludes that the accident airplane entered the D6 maintenance check with an elevator control system that was rigged to achieve full elevator travel in the downward direction. The Safety Board further concludes that the accident airplane's elevator control system was incorrectly rigged during the D6 maintenance check and that the incorrect rigging restricted the airplane's elevator travel to 7° AND, or about one-half of the downward travel specified by the airplane manufacturer.
- The only visible sign of the mis-rig during the first officer's external preflight inspection would have been a change in the elevator resting position. The normal elevator resting position is between 14° and 15° AND; after the mis-rig, the elevator resting position was about 7° AND. Because the horizontal stabilizer on a parked Beech 1900D is located about 15 feet above the ground, it would be difficult to detect the change in the elevator resting position from the ground. [ . . . ] The Safety Board concludes that the changes in the elevator control system resulting from the incorrect rigging were not conspicuous to the flight crew.
- The Safety Board concludes that the RALLC quality assurance inspector did not provide adequate OJT and supervision to the SMART mechanic who examined and incorrectly adjusted the elevator control system on the accident airplane.
- The Beech 1900D elevator control system rigging procedure (section 27-30-02) does not include provisions for adjusting cable tension as an isolated task. However, the mechanic decided to adjust the cables as an isolated task and, as a result, did not follow each step included in the rigging procedure. The quality assurance inspector was aware that the mechanic was selectively performing steps from the rigging procedure and that he was only adjusting cable tension. In fact, the inspector stated, during a post accident interview, that he did not think the manufacturer intended for mechanics to follow the entire rigging procedure and that the entire procedure had not been followed when past cable tension adjustments were made.
- The mechanic skipped nine applicable steps in the Beech 1900D elevator control system rigging procedure (see section 126.96.36.199).130 One of these steps indicated that, for airplanes equipped with an F-1000 FDR, the pitch position potentiometer needed to be calibrated (step u). The mechanic was required to perform this step because the accident airplane had an F-1000 FDR installed. Step u indicated that, to calibrate the pitch position potentiometer, the mechanic needed to perform the FDR pitch adjustment procedure described in another section of the Beech 1900D AMM. This procedure referred the mechanic to a table that specified eight different elevator settings, ranging from 14° AND to 20° ANU (including 0°), and instructed the mechanic to record the FDR readout for these settings. The mechanic, however, would not have been able to move the elevator to the first setting, 14° AND, because elevator travel was restricted to about 7° AND.
- The performance of step u would have likely alerted the mechanic or the quality assurance inspector that the elevator control system was not properly rigged. However, the mechanic indicated that he skipped step u because he thought the calibration did not need to be done. The quality assurance inspector stated that he did not think that an FDR was installed on the airplane, but the inspector should have known that the airplane was equipped with an FDR because most, if not all, Beech 1900D airplanes were outfitted with an FDR. Also, the inspector could have easily determined that the airplane was equipped with an FDR. Specifically, the wiring and the sensor for the FDR were in the same area of the airplane where maintenance was being performed. Also, the FDR unit is mounted in the forward (AFT1) cargo compartment and is readily visible. In addition, a circuit breaker for the FDR is located in the cockpit.
- The post maintenance checks performed by the quality assurance inspector and the mechanic were not adequate to detect the elevator control system mis-rig [ . . . ] A functional check at the end of the procedure would have provided a more comprehensive, systematic, and direct method to ensure that any mis-rigging problem was caught before an airplane was returned to service. Such a functional check would consist of a mechanic in the cockpit pushing the control wheel full forward and then pulling the wheel full aft while another mechanic, who was at eye level with the horizontal stabilizer, measured the position of the elevator using a travel board. This process would determine whether the elevator achieved the correct deflection for the full forward and full aft movement of the control column.
[NTSB AAR-04/01, ¶2.4]
- The airplane performance study for flight 5481 determined that the accident airplane's actual weight was about 17,700 pounds and that its actual CG position was about 45.5 percent MAC. As a result, flight 5481 had exceeded the Beech 1900D certified weight limit of 17,120 pounds and the certified aft CG limit of 40 percent MAC.
- The restricted elevator travel alone and the aft CG alone would not have been sufficient to cause the uncontrolled pitch up that led to the flight 5481 accident. The Safety Board concludes that flight 5481 had an excessive aft CG, which, combined with the reduced downward elevator travel resulting from the incorrect elevator rigging, rendered the airplane uncontrollable in the pitch axis.
[NTSB AAR-04/01, ¶3.1]
- The accident airplane entered the detail six maintenance check with an elevator control system that was rigged to achieve full elevator travel in the downward direction.
- The accident airplane's elevator control system was incorrectly rigged during the detail six maintenance check, and the incorrect rigging restricted the airplane's elevator travel to 7° airplane nose down, or about one-half of the downward travel specified by the airplane manufacturer.
- The changes in the elevator control system resulting from the incorrect rigging were not conspicuous to the flight crew.
- The Raytheon Aerospace quality assurance inspector did not provide adequate on-the-job training and supervision to the Structural Modifications and Repair Technicians mechanic who examined and incorrectly adjusted the elevator control system on the accident airplane.
- Because the Raytheon Aerospace quality assurance inspector and the Structural Modifications and Repair Technicians mechanic did not diligently follow the elevator control system rigging procedure as written, they missed a critical step that would have likely detected the mis-rig and thus prevented the accident.
- A complete functional check at the end of maintenance for critical flight systems or their components would help to ensure their safe operation, but no such check is currently required.
- Flight 5481 had an excessive aft center of gravity, which, combined with the reduced downward elevator travel resulting from the incorrect elevator rigging, rendered the airplane uncontrollable in the pitch axis.
- When an inspector provides on-the-job training for a required inspection item (RII) maintenance task and then inspects that same task, the independent nature of the RII inspection is compromised.