Page 26 - Volume 13 Number 5

and which is the weaker by having one running and the other not running.
“Uh, wait a minute, Tom. You are discussing a situation in which both engines are consuming fuel from one nacelle tank. But that is a violation of a POH limitation. We can only crossfeed when an engine is shutdown in flight!”
You are exactly right: Most POHs do indeed contain this Fuel System Limitation. From an engineering design standpoint, however, I am also right. Namely, the size of the crossfeed line and the supply capability of the boost pump allows for both engines to be fed from one side’s nacelle tank. Please realize, as has been stated by me in previous articles that the POH’s crossfeed limitation comes from legal, not engineering, concerns. Let’s look at this in a bit more detail.
Suppose that one day the FBO’s Jet-A truck breaks down after it had topped the filler caps on the left side but had not yet finished filling the right side. We are left with, say, a 500-pound imbalance. The 300-series has a 300-pound imbalance limitation and the C90B and C90GT-series have a 200-pound limit. (Both of which, in my opinion, are unnecessary.) For the other models, we are still good to go with the 500-pound imbalance. So off we go – with a little aileron trim cranked in – and when safely in cruise we decide to balance the fuel. We do this by crossfeeding, sending fuel from the side with more fuel to both engines until the greater fuel quantity equalizes with the lesser quantity. Step 1: Make sure the electric pump on the feeding side is on. Step 2: Open the crossfeed valve. Step 3: Make sure the electric pump on the other side is off. Step 4: Monitor the fuel quantity gauges over a period of at least 15 to 30 minutes to verify that indeed the side with more fuel is going down and the side with less fuel is not changing. Step 5: Keep monitoring fuel quantity and stop crossfeeding when balance is achieved!
OK, I admit it. You caught me again, caught me in not following the manufacturer’s checklist. Realize that this article is meant to cover every King Air model. The individual differences are many. For example, in the F90-, 200-, and 300-series, moving the crossfeed switch laterally toward the side to which you want to feed the fuel not only should send power to the NC crossfeed valve and cause it to open but also should turn on the feeding side’s standby pump. It does not, however, turn off the receiving side’s standby pump if it happened to be already on. Another example of differences: In the C90 and earlier style systems the pilot will definitely have to turn off the receiving side’s boost pump since it is normally running at all times. The E90, A100, and B100 probably follow the procedure written above most accurately.
But realize this, readers: There is never a Step 4 or Step 5 in the POH and they are both critically important!
24 • KING AIR MAGAZINE
There is absolutely no way to truly know that fuel is going from the high side to both engines until the decrease in the higher fuel level is confirmed! Does the POH address this? No! Have you been taught this? Maybe.
As for Step 5, this is where most of the legal team’s liability worries arise. Suppose that an asleep-at-the- wheel pilot gets distracted and fails to stop crossfeeding when balance is achieved. In fact, he forgets the fuel panel totally and runs the feeding side’s nacelle tank dry. Since this tank is feeding both engines, they both quit nearly simultaneously! Darn! I hate it when that happens!
“But wait!” says our hapless pilot. “I still have fuel on the other side. I’ll use that to get the engines running again!”
Quiz time: Is it easier for the engine-driven pump to suck vapor (air) or liquid (fuel)? I think we can all agree that the engine-driven pumps will draw air before fuel. Only if we turn on the electric boost pump/standby pump on the side with fuel remaining – so that our common fuel manifold, our crossfeed line, is full of pressurized liquid and no air – do we have a chance for an airstart to be successful. Hard to do? No! A critical step that is easy to overlook? Yes!
Now let’s review the “proper” use of crossfeed. Suppose we are returning from Europe and on our leg from Reykjavik to Goose Bay we lose oil pressure and shut down the right engine. The airports in Greenland are below minimums and we have enough fuel to continue to Goose Bay. (By the way, in most cases our range just went up, not down!) As we continue with only the left engine running, the left fuel is decreasing while the right fuel is remaining at the level it had when the engine was secured.
When the left side gets down to, say, 500 pounds, but with the right side still showing 800, we decide to send the fuel from the right side to the left engine. Easy. Right boost pump on, crossfeed open, left boost pump off. Now the right fuel quantity starts decreasing and the left fuel quantity does not change ... just as it should.
A reminder: For you fortunate pilots flying a member of the F90-, 200- or 300-series, the “right boost pump on, crossfeed open” steps mentioned above are both done by merely moving the crossfeed switch left toward the engine we wish to feed.
“But wait, something’s wrong! The right fuel pressure warning annunciator is still illuminated!” Relax. That’s normal. When you conduct your first-flight-of-the-day fuel panel checks it is correct for both left and right fuel pressure annunciators to extinguish. But with the right engine actually shutdown and all of the proper checklist “cleanup” steps completed, the right Fuel Firewall Shut- off Valve has been closed. Thus, the pressure from the operating pump cannot be felt at the pressure switch
MAY 2019