N441VB

HISTORY OF FLIGHT

On August 20, 2008, about 1230 eastern daylight time, a Cessna 441, N441VB, was substantially damaged when it departed the left side of runway 33R during an aborted takeoff at Baltimore/Washington Thurgood Marshall Airport (BWI), Baltimore, Maryland. The pilot/owner and the three passengers were uninjured. The personal flight was operated under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed.

According to the pilot, the inbound flight to the airport, as well as the accident flight preflight procedures, start-up and taxi-out were normal. However, as the airplane accelerated during the takeoff roll, it moved "slightly to the left" on the runway. The pilot "added power on the left engine," but the airplane continued to the left, and the left wheel departed the left edge of the runway pavement. The pilot aborted the takeoff, and continued to correct the direction of travel by manipulating the engine power levers. The airplane continued to veer to the left, completely departed the paved surface, and struck an earthen mound in the grass. The nose landing gear fractured, and the airplane came to rest approximately 2,500 feet beyond the start of the takeoff roll. The pilot shut down the airplane, and all occupants exited via the main door. BWI airport rescue and fire fighting personnel and equipment responded to the scene, and partially foamed the airplane to prevent a fire.

PERSONNEL INFORMATION

According to Federal Aviation Administration (FAA) and pilot-provided records, the pilot held a private pilot certificate with airplane single-engine land, multi-engine land, and instrument ratings. The pilot reported 2,485 total hours of flight experience, including 1,473 hours in the accident airplane make and model. He reported 3, 27, and 55 hours respectively, in the 30, 60, and 90 days preceding the accident, all of which were in the accident airplane. The pilot's most recent flight review was completed in April 2008, and was conducted in a Cessna 441 "flight simulator." His most recent FAA third-class medical certificate was issued in March, 2007.

AIRCRAFT INFORMATION

The airplane was a low-wing turboprop equipped with two Garrett TPE331-10N turbine engines and McCauley "BlackMac" four-blade, full-feathering, reversible propellers. According to FAA records, the airplane was manufactured in 1980, and was purchased by the current owner in 2000. The most recent 100 hour inspection was completed in February 2008, when the airplane had a total time in service of 3,963 hours.

Engine and Propeller Controls

The principal engine and propeller controls included a power lever and a condition lever for each engine/propeller. Each engine was equipped with a dedicated fuel computer and fuel control unit. The power and condition levers for each engine were electrically linked to the fuel computer for that engine, which in turn was electrically linked to the engine's fuel control unit. The power lever for each engine was also mechanically linked to the engine's fuel control unit.

The engine had two operating modes, "normal" and "manual." In the normal engine operating mode, pilot input commands were processed by the fuel computer, which in turn provided input to the fuel control unit to regulate engine speed. A cockpit switch for each engine could be used to select the manual mode for that engine. Selection of the manual mode deactivated the engine fuel computer, and engine speed was then regulated directly by the pilot's manipulation of the power lever, and the resulting mechanical input to the fuel control unit. The accident takeoff attempt was conducted with the engine switches in the "normal" mode.

The two operating modes for each propeller were "beta" and "propeller-governing," and the power levers were used for control in both modes. Beta mode was for propeller blade angles from flat pitch through reverse, and was to be used only during ground operation. In the beta mode, the power lever hydraulically controlled the propeller blade angle. In the propeller-governing mode, which was to be used for flight, the power lever controlled fuel flow either electrically (in normal mode, fuel computer active) or hydro-mechanically (manual mode, fuel computer inactive), and the propeller governor regulated propeller blade angle by hydraulic actuation. Governor oil pressure was used to drive the propeller blades in the fine pitch direction. The condition levers were used to set the appropriate governor target propeller rpm as a function of the airplane operating regime.

Propeller Start Locks

Each propeller blade was equipped with a propeller start lock. According to the airplane manufacturer's maintenance manual, "When the engine is shut down and propeller governor oil pressure decreases, the blades will be driven into a feathered position by a spring." The purpose of the start locks was "to prevent this procedure by holding the blades in a low pitch position for successful engine start."

The start locks were actuated by centrifugal force, and would "engage when the propeller is moved to reverse immediately following fuel cutoff at shutdown." The airplane manufacturer's information manual, which was a document for pilots that incorporated information from the pilots operating handbook and the FAA-approved airplane flight manual, stated that, "Before starting the engines, the propeller blades must be on the start locks [blades in low pitch]. This is required to minimize propeller drag and resultant high turbine temperatures during the start [hot start]. Additionally, the start locks provide the only means by which the propeller can be set for a functional check of the overspeed governor." The information manual also stated that "if the start locks are not engaged before starting, they can be engaged by actuating the unfeathering pump switch with the power lever in full reverse."

The information manual further noted that the start locks could be "disengaged after start by moving the power lever toward reverse after engine start." This action would unload the start lock mechanism, allow the start lock to disengage, and permit the propeller blade pitch to be varied for subsequent taxi and flight operations.

A representative of the propeller manufacturer stated that if the start lock remained engaged after the engine was started, a commanded increase in power would result in a propeller overspeed "once the governed blade angle needs to exceed the start lock blade angle. There will be zero psi [governor oil pressure in pounds per square inch] at the prop[eller] (and pressure switch) since the governor’s correction for overspeed is to drop oil pressure to coarsen [blade] pitch."

Cockpit Annunciator Panel

The airplane was equipped with an annunciator panel that was located below the glareshield on the center instrument panel, and which consisted of 20 individual, colored annunciator lights for each engine. According to Section 7 (Airplane & Systems Descriptions) of the information manual, the purpose of the panel was to "annunciate items of interest to the pilot in the applicable color of red, amber, green or white." The information manual also stated that "When a hazardous condition exists, requiring immediate corrective action, a red warning light will illuminate. When an impending possibly dangerous condition exists, requiring attention but not necessarily immediate action, an amber light will illuminate. A green or white light will illuminate to indicate a safe or normal configuration..." The airplane was also equipped with a press-to-test button in the center of the annunciator panel that could be used to verify the functionality of the lights.

Beta Light Operation

According to the information manual, the left and right beta lights in the annunciator panel were amber in color, and the purpose of each was to advise the pilot that "the propeller is capable of being reversed." The guidance also stated that illumination of the beta lights was "normal during ground operation."

According to the maintenance manual, "beta mode occurs whenever fuel flow is reduced by moving the power lever aft of FLIGHT IDLE, and engine power will not maintain engine speed at the propeller blade angle selected." The maintenance manual also stated that, "engines operate in beta mode during all normal ground handling [taxi] operations," and, "In beta mode, the power lever controls propeller blade angle. Beta mode operation requires high oil pressure to the propeller which sets blade angle to the pitch control minimum setting. This is accomplished by decreasing engine fuel flow with the power lever until the propeller load decelerates the engine below the propeller governor setting (underspeed). When the [condition lever is set to "START AND TAXI" and the] power lever is moved aft of the flight idle detent, the fuel control computer resets the propeller governor to 106 percent RPM which instantly increases propeller governor output pressure (beta pressure)," enabling propeller operation in the beta range (blade angles from zero to reverse pitch). Finally, the maintenance manual stated that, "A sensor between the propeller governor and the propeller pitch control illuminates the beta light when the propeller governor produces sufficient oil pressure to operate in the beta mode."

According to the propeller manufacturer representative, the beta light activation system was strictly a function of a governor oil pressure sensing switch, and the system was not equipped with any direct sensors or circuitry regarding the status or position of the start locks. During engine start and taxi, whenever the power lever(s) were set to flight idle power or slightly above, the beta light(s) would always be illuminated, regardless of whether the start locks were engaged or disengaged.

Airplane Normal Procedures

The airplane ...