Page 20 - January 2015 Volume 9, Number1

Ask the Expert Fuel Crossfeed...
Why Can’t We Do It?!
by Tom Clements
Every Pilot’s Operating Handbook (POH) for the various King Air models contains a prohibition against using crossfeed except when one engine is inoperative. In the case of the A90, B90, and C90 variants, the POH also allows crossfeed when one side’s boost pump is inoperative.
This prohibition means that we are not allowed to crossfeed (1) to correct a fueling imbalance, side-to- side, or (2) to consume the remaining fuel as rapidly as possible from a side that has sprung a large leak. Why can’t we do this? Why are we prevented from taking advantage of this desirable option in these two cases?
The crossfeed prohibition did not exist until after the POHs got revised in the mid- and late-1970s. Prior to that, pilots could and did use crossfeed as needed to correct a fueling imbalance. The case of a major tank leak is so rare – and probably only of great concern when far from land on an oceanic ferry flight – that I will not address it again in this discussion.
In fact, all King Air models, including the latest 350 variants, are designed and manufactured with sufficient pump capacity and fuel line capacity that feeding both engines from one side’s fuel supply can physically be done, even during periods of maximum fuel flow. Knowing this, it is apparent that the crossfeed limitation did not originate with the engineering designers; instead it came from Beech’s legal team.
In June 1974, a Beechcraft BE95 Travel Air – the 180 horsepower Lycoming-powered predecessor to the Baron – experienced fuel starvation to both engines, crashed, caught fire, and killed the four occupants. Investigation revealed that both engines had been drawing fuel from the same tank on one side, the exhaustion of which led to the double engine failure. The fuel selectors were positioned properly for this crossfeed situation. The pilot never repositioned the fuel selectors such that he could feed the engines from the existing fuel in the other tanks.
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Although most aviation-savvy people thought this was an obvious case of pilot error, a jury trial found Beech to be liable for a “Failure to Warn.” Huh? I guess the jury thought there should be something like, “Thou shalt not feed all engines from one tank, run said tank dry, and not utilize the remaining fuel in other tanks!”
That tongue-in-check type of warning never got inserted into revised POHs, but the crossfeed prohibition we have lived with ever since came as a direct response to this infamous legal case.
A chapter in my “The King Air Book” discusses the C90’s fuel system in depth and one of the discussion points therein tries to highlight the absurdity of prohibiting crossfeed except with an engine out, while at the same time allowing the feeding of both engine’s from one fuel supply following a boost pump failure. In other words, the fuel system designers specifically intended feeding both engine’s from one supply while the lawyers, later, told them not to do so.
The fact is that any King Air’s fuel system can supply fuel to both engines from one side’s nacelle tank. It is quite obvious that the degree of risk has gone higher when this is done, since fuel contamination or exhaustion (of that tank) will affect both, not just one, powerplant. Realizing that increased risk, I am sure that few, if any. pilots would choose to feed both engines from one tank while near the ground: During takeoff, initial climb, approach, and landing. On the other hand, I believe most pilots would be willing to accept the increased risk while established in cruise at an altitude high enough to permit glide and airstart procedures in the event the unlikely happened.
The actual fuel imbalance limitation varies widely among the various King Air models, from no limitation being stated to a high of 1,000 pounds in the 200-series and to a low of 200 pounds in the C90B and later 90 models. Unless the fuel load can be equalized between the two sides, it means that our endurance and range
JANUARY 2015