Page 13 - Volume 12 Number 8

If the vernatherm inside the oil-to-fuel heater is bad, it continues to heat the fuel as if the aircraft was at altitude and not on the ground with a triple digit OAT. This doesn’t allow the FCU to function and the engine will not make power.
shut off the oil-to-fuel heater during extreme heat conditions. If this vernatherm is bad, then the oil-to-fuel heater doesn’t get the message to shut off, so it continues to heat the fuel as if the aircraft was at altitude and not on the ground with a triple digit OAT. Super-heated fuel lacks the correct viscosity, and the FCU does not know what to do with it. The FCU cannot function and the engine will not make power.
There are a number of factors that contribute to this scenario: (A) You are on the ground, it’s really hot outside, and the heat radiating off the ramp can be 140o F, so your oil temperature is already up there. (B) If you are in a King Air 200 with 4-blade props you no doubt have your ice vanes deployed (down) to protect against FOD, but this also opens the rear bypass door and prevents airflow across the oil-cooler; now your oil temp climbs even higher. (C) You taxi out, maybe you sit in line waiting to take off, and if the vernatherm in your oil-to-fuel heater is not working, the fuel becomes super-heated and the engine won’t make power. So, you taxi back to the ramp in hopes of finding some maintenance.
AUGUST 2018
To make matters worse, the problem could appear intermittent because in the time it took to find some assistance, everything has cooled off just enough to work properly. As soon as you get a mechanic there to diagnose the situation, you fire up the problem engine and everything works just fine! OK, you think it was just some glitch so you load everyone back in the aircraft, taxi back out to the runway and again, no power on that engine.
Troubleshooting
The most expedient way to troubleshoot the oil-to- fuel heater is to run the engine for about 10 minutes; shut down and open up the R/H rear cowl door. You are going to check the temperature of the fuel bowl on the high-pressure fuel pump. The HP fuel pump will be just forward of the FCU and its fuel bowl is above the oil-to-fuel heater (see photo, opposite page). BE CAREFUL! If the vernatherm in the oil-to-fuel heater is not working, this fuel bowl will be hotter than a poker!
KING AIR MAGAZINE • 11