C4202 "Fam 10" |
Loss of useful power (either a rollback or compressor stall): Engine malfunctions may result in a loss of useful power where the power available is insufficient to prevent the high rates of descent associated with low power/low propeller blade pitch situations. To determine whether or not the propeller should be feathered, check the VSI while descending at 100 KIAS clean. A descent rate in excess of 600-800 fpm will require the propeller to be feathered. The best glide performance power setting at 100 KIAS, aircraft clean, is 205 ft-lbs.
Fuel control rollback
Condition |
Torque |
N1 |
ITT |
Prop RPM |
FF |
Temp |
Pressure |
Rollback |
low |
40-62% |
decaying |
<2200 |
80-100 PPH |
normal |
normal |
Reduced fuel flow (rollback) is typical of a fuel control unit pneumatic sensing system malfunction. If engine will not respond to PCL movements and ITT and N1 indicate the engine is running at a very low power settings, advance the EPL in an attempt to regain control of engine power by use of the manual fuel control system. N1 40-62% - indicating a "rollback" (fuel control unit stuck at minimum flow), proceed as follows:
Compressor stall - Compressor stalls may be characterized by an audible change in engine noise (a loud bang or backfire) with fluctuations in torque, ITT, N1, and fuel flow. Additionally, flames and smoke may be visible from the engine exhaust stacks. A severe compressor stall may result in engine damage and/or flameout. Compressor stalls may be caused by damaged or degraded compressor or turbine blades, disrupted airflow, or compressor bleed valve malfunction. If compressor stalls occur, proceed as follows:
Emergency power lever (EPL) - The manual fuel control system consists of a cockpit control which provides the pilot with direct mechanical linkage to the bellows and the fuel metering pin in the FCU. The manual fuel system is a backup system only and is used in the event of a malfunction in the pneumatic section of the FCU.
When engaged, the system will bypass all pneumatic failure modes which result in minimum fuel flow and/or lack of engine response to PCL movement. Movement of the emergency power lever (EPL) toward max, mechanically depresses the bellows to schedule more fuel to the engine. This system relies on torque tube pretension to reduce power as the EPL is moved toward the idle range. When using the EPL, normal operation of the landing gear warning system is provided.
If loss of power occurs due to a malfunction of the FCU, power may be restored using the EPL. No automatic fuel scheduling is incorporated, and fuel metered to the engine is a direct function of the lever position. Idle RPM, when required, should be maintained above 65% N1 by the pilot to eliminate the lack of EPL response in the idle range, and improve engine response. The manual fuel control system bypasses the protective devices relying on pneumatic bleed air as the operational parameter for the fuel topping function of the primary governor. Failure of the FCU at high power cannot be corrected with the EPL.
NOTE - With gear up, normal operation of the gear warning system occurs when the PCL and the EPL are retarded below 75% N1. Additionally, the warning system will activate (with gear up) when both the PCL and EPL are forward of the 75% switch.
CAUTION - Compressor stall, vibrations and overtemp are probable with rapid accelerations of the EPL, particularly at the low-end of the power spectrum.
CAUTION - During an actual rollback, if power is restored with the EPL, exercise caution not to excessively reduce power in the final landing transition, as sink rate will drastically increase at low power.
Common errors:
1) Failure to check condition lever at full increase.
2) Failure to operate the EPL smoothly on activation.
3) Failure to monitor power settings during changes in altitude.
4) Using the PCL for operation of the manual fuel system after EPL is engaged.
Primary governor failure
Normally, the primary and overspeed governor and fuel topping function will act in sequence to hold propeller rpm within suitable range to continue flight or to reach a suitable repair facility. If the propeller is being governed by the fuel topping governor alone, expect moderate surges in propeller rpm, N1, torque and fuel flow as fuel topping activates and deactivates.
Propeller Speed Above 2200-2332 RPM / 2332+ RPM
1. Attempt to adjust rpm to normal operating range by manipulation of the Condition
Lever.
If normal indication is restored
2. CONTINUE FLIGHT / Land ASAP using NORMAL procedures
(if 2332+ RPM)
If adjustment of the Condition Lever fails to produce normal propeller
response
3. Land ASAP using PEL procedures.
CAUTION - Advancing the EPL beyond the point at which the fluctuations are minimized will aggravate the overspeed condition.
NOTE - If activation of the primary fuel topping governor has occurred, Py air will be bled automatically and fuel flow will be reduced towards minimum, causing corresponding fluctuations in N1, torque, fuel flow, and prop rpm as rpm surges to 2398 and is then reduced again by the fuel topping function. Engaging the EPL will lessen the severity of low-end fluctuations.
Uncommanded Propeller Feathers
NOTE - In the event of a primary governor shaft failure, the propeller will move toward feather; however, unboosted engine oil pressure alone may be sufficient to maintain propeller pitch between feather and normal governing rpm range at high-power settings. Resultant power may be sufficient to maintain level flight.
NOTE - Because it is feasible for the propeller to unfeather and restore useful power, consideration should be given to leaving the condition lever at FULL INCREASE RPM until intercepting the emergency landing pattern (ELP).NOTE - Generator power will not be available after engine shutdown.
Propeller RPM fluctuations
Propeller rpm fluctuations caused by fluctuating blade angle will be accompanied
by a corresponding torque flux and will be audible. Propeller rpm fluctuations
may be caused by a faulty propeller overspeed governor test circuit or a malfunctioning
primary governor. A malfunctioning primary governor may be caused by metal particles
in the oil system and may therefore be the precursor to a chip light.
Use of the EPL (see discussion items)
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