Page 20 - Nov 2015 Volume 9, Number 11

the accumulator tank and the fuel manifold – then fuel can partially or totally fill the accumulator, displacing the necessary volume of air needed to provide the proper “shot,” providing the same result, smoking and coking.
There is a third problem that’s rare, but not unheard of. Namely, what if both check valves leak at the same time? Now the fuel that can migrate from the manifold into the accumulator tank can also find its way into the P3 air system. It can lead to a strong kerosene smell coming into the cabin from the environmental bleed air inflow, most noticeable when high power is added during takeoff.
The last few E90s (LW-334 through LW-347), as well as all of the F90s after LA-58 (but not the F90-1s) almost always exhibit smoking at shutdown even when everything is working properly. Why? Because these models have a unique FCU, unlike the FCU installed in other models. Instead of a single fuel line going from the FCU to the Flow Divider/Dump Valve where it then feeds the primary and secondary manifolds, the -28s on the E90 and the -135s on the F90 have two fuel lines exiting the FCU, going to a device called the Start Control, mounted on the aft accessory case. The Start Control does the sequencing of fuel to Primary and Secondary manifolds and also contains the shutoff valve operated by the Condition Lever. Two lines exit the Start Control to connect to the manifolds, and each of these lines is over two feet long. What this means is that there is a lot more fuel line volume and
more residual fuel that must be purged at shutdown, yet the accumulator tank is exactly the same size as in all the other models. I am convinced there is an insufficient air charge to properly purge the last bit of fuel through the nozzles...such that smoking is almost inevitable.
There is a straightforward, but rather odd, procedure that should be used for the E90s and F90s with the bleed air purge system and this same procedure can be used on other models that exhibit smoking until check valve problems can be addressed and corrected. What’s the procedure? Merely have the ignition exciters sparking during shutdown by moving the Auto-Ignition switches to Arm before pulling the Condition Levers into Cut-off. Remember to turn Auto-Ignition off before leaving the cockpit. Having the ignition sources active at shutdown allows the dribbling fuel to be ignited and burned, solving the smoke issue.
All 300s and 350s were manufactured with the Bleed Air fuel purge system, none having a fuel drain collector system.
The P3 accumulator will not have enough pressure to provide adequate fuel manifold purging if N1 has never reached a high level. It is very common to see some smoke if the engine is started, reaches only idle speed, and is then shutdown.
Some of our readers have experience with the Honeywell (nee Garrett) TPE331 turboprop engine,
Prop & Wing Boots for General Aviation Aircraft
Faster.
48 hour delivery - Guaranteed
Better.
Longer Lasting - Proven
Smarter.
Better Value for your Money
For more information visit www.iceshield.com or call 1-800-767-6899
18 • KING AIR MAGAZINE
NOVEMBER 2015