Aircraft and engine limits are described in the Limitations section of the POH (Figure 7-24). These limitations have been approved by the Federal Aviation Administration and must be observed in the operation of the King Air 350.
The ENGINE OPERATING LIMITS chart g i v e s t h e m a j o r o p e r a t i n g l i m i t s.
Th e P OW E R P LA N T I N ST RU M E N T MARKINGS chart lists the minimum, normal, and maximum limits. Figure 7-20 for a l i s t i n g o f t h e o p e r a t i n g r a n g e s f o r
TAKEOFF 100 (10) 820 104 1700
(9) 90 to 135 0 to 110
TRANSIENT 156 (8) 850 (8) 104 1870
(8) 200 0 to 110
FOOTNOTES:
(1) Torque limit applies within range of 1000 - 1700 propeller rpm (N2). Below 1000 propeller rpm, torque is limited to 62%.
(2) Normal oil pressure is 90 to 135 psi at gas generator speeds above 72%. With engine torque below 62%, minimum oil pressure is 60 psi at normal oil temperature (60 degrees to 70 degrees C).
Oil pressures under 90 psi are undesirable. Under emergency conditions, to complete a flight, a lower oil pressure limit of 60 psi is permissible at a reduced power, not to exceed 62% torque. Oil pressures below 60 psi are unsafe and require that either the engine be shut down or a landing be made at the nearest suitable airport, using the minimum power required to sustain flight.
Fluctuations of plus or minus 10 psi are acceptable.
During extremely cold starts, oil pressure may reach 200 psi. In flight, oil pressures above 135 psi but not exceeding 200 psi are permitted only for the duration of the flight.
(3) A minimum oil temperature of 55°C is recommended for fuel heater operation at take-off power.
(4) Oil temperature limits are -40°C and +110°C. However, temperatures between 99°C and 110°C are limited to a maximum of 10 minutes.
(5) This value is time limited to 5 seconds.
(6) High ITT at ground idle may be corrected by reducing accessory load and/or increasing N1 rpm.
(7) Cruise torque values vary with altitude and temperature.
(8) These values are time limited to 20 seconds.
(9) To account for power setting accuracy and steady state fluctuations, inadvertent propeller RPM excursions up to 1735 RPM are time limited to 7 minutes.
(10) To account for power setting accuracy and steady state fluctuations, inadvertent torque excursions up to 102% is time limited to 7 minutes.
Figure 7-24. Engine Limits Chart
7 POWERPLANT
During engine start, temperature is the most critical limit. The ITT starting limit of 1,0 0 0°C is limited to five seconds. For this reason, it is helpful during starts to keep the condition lever out of the LOW IDLE detent so that the lever can be quickly pulled back to FUEL CUTOFF.
Monitor oil pressure and oil temperature.
During the start, oil pressure should come up to the minimum 60 psi quickly, but should not exceed the maximum of 200 psi. During normal operation the oil temperature and pressure should be green, from 90 to 135 psi.
Fluctuations of ± 10 psi are acceptable.
O i l p re s s u re b e t w e e n 6 0 a n d 9 0 p s i i s undesirable; it should be tolerated only for completion of the flight, and then only at a reduced power setting.
Oil pressure below 60 psi is unsafe; it requires that either the engine be shut down or that a landing be made as soon as possible using minimum power required to sustain flight.
A minimum oil temperature of 55°C is r e c o m m e n d e d f o r o i l - t o - f u e l h e a t e r operation at takeoff power. Oil tempera-ture limits are –40°C and +110°C during IDLE, and 0°C to +110°C during normal o p e r a t i o n s. H o w e v e r , t e m p e r a t u r e s between +99°C and +110°C are limited to a maximum of 10 minutes.
During ground operations, ITT tempera-tures are critical. They can be controlled by the N1rpm, air conditioning, P3use, and the generator load. With the condition levers at LO IDLE, high ITT can be corrected by reducing the generator and other N1loads, then increasing the N1 rpm by advancing the condition levers. The air conditioner, for example, draws a heavy load on the r i g h t e n g i n e N1. I t m a y h a v e t o b e temporarily turned off.
At approximately 70% N1 rpm, the HI IDLE condition lever position normally reduces the ITT. Once ITT is reduced below
the IDLE limit of 750°C, the N1loads may be restored as desired as long as ITT stays b e l o w 7 5 0 ° C . D u r i n g n o r m a l f l i g h t o p e r a t i o n s, t h e I T T s h o u l d n e v e r b e allowed to exceed the maximum continu-ous limit of 820°C .
During the climb, torque decreases; ITT may increase slightly. The cruise climb ITT limit is not placarded. Torque, ITT, N1, and propeller limits are the same in maximum cruise as they are for takeoff; however, cruise torque values vary with altitude and temperature.
Transient limits provide buffers for surges during engine acceleration. Torque and ITT have an allowable excursion duration of 20 seconds. A momentary peak of 156%
and 850°C is allowed for torque and ITT respectively during acceleration.
Th e OV E RT O R Q U E L I M I T S c h a r t (Figure 7-25) shows actions required if t o r q u e l i m i t s a r e e x c e e d e d u n d e r a l l conditions. If the torque limits are exceeded for more than a few minutes, the gearbox c a n b e d a m a g e d . Th e c h a r t s h o w s t h e specific limits and action required if they are exceeded.
Figure 7-25. Overtorque Limits
The Generator Limits table in the POH s h o w s l i m i t s f o r g ro u n d o p e ra t i o n a t various N1rpms. Any time these limits are e x c e e d e d , t h e a c c e s s o r y l o a d m u s t b e reduced or N1increased to the limits shown in the table. A generator load of 75% is maximum for ground operation at an N1of between 62% and 70%.
The Inflight limits are 100% generator load from sea level to 34,000 feet. Above 34,000 feet, maximum sustained generator load limit is 95%. Maximum continuous and maximum cruise share the same generator limits, but due to N1loading, certain limits must not be exceeded as indicated in the Before Takeoff (Final Items) checklist in the POH.
The overtemperature chart (Figure 7-26) shows the specific actions required if ITT l i m i t s a r e e x c e e d e d d u r i n g s t a r t i n g conditions. For Area A, determine and correct the cause of overtemperature. If it is during a start, have the engine visually inspected through the exhaust duct, then record the action in the engine logbook (Figure 7-27).
Overtemperature in Area B requires that a hot section inspection be performed. During a hot section inspection, the combustion chamber and turbine areas and components are examined and replaced. Parts should be repaired or replaced as necessary.
7 POWERPLANT
Figure 7-26. Overtemperature Limits
Figure 7-27. In-Flight Engine Data Log
In Area C, overtemperatures may require that the engine be returned for overhaul.
Exceeding ITT limits in this area for more than a few seconds may cause extensive engine damage.