As a new group of pilots enter the world of King Air® aviation, it is essential to address a subject that, while widely known, remains not fully understood. PLM is not something that happens on every King Air®. There is no model, age, or airframe hours that would indicate a particular King Air® should or should not have 'the tendency.' Should you have a PLM episode, do NOT rely on autofeather (AF) to help. If you don't know why that is true, your instructor did you a disservice.
The topic has been extensively discussed, including a notable presentation by Tom Clements at the King
Air Gathering a few years ago. PLM often occurs when the checklist is not followed, particularly after
maintenance.
One might assume that mechanics would return the aircraft to its original state after maintenance, but
this is rarely the case. Mechanics need to fully loosen the friction locks (FL) on the throttle quadrant
power levers (PL) to move the fuel control unit (FCU) linkage out on the engine. Unfortunately, these
locks are sometimes not tightened before being released.
At King Air® Academy, we often say, “If you have flown one King Air®, you’ve flown one King Air®" which
holds particularly true for PLM. We have observed significant variations in PL behavior among the same
aircraft model. For instance, we have videos of two aircraft, in the same fleet, within a few serial
numbers where one aircrafts power lever does not move and the other will snap back to flight idle when
the FLs are loosened.
How to know if the King Air® you fly has PLM ‘tendency’. The easiest way, without the engines running, is
to tighten the FL, push the PLs all the way forward, and then slowly loosen the FLs one lever at a time. If
you can fully loosen the FL locks without any movement in the levers, you may still have PLM. This
simple ground test is not foolproof but provides a good initial indication. On the ground without the
engines running and no vibration, no gear movement or air loads is just a simple test to know if your
aircraft has 'the tendency'. This is not a sure fire test for PLM. The next test you may want to try and
some point is the same test but in cruise (probably a deadhead leg). The PLs may be at full forward
position, however if you loosen one FL at a time, you will see if either the left or right PL rolls back. Most
all find it is the left PL that migrates. If the right PL even moves, it tends to be very little. Again, this just
demonstrates if your aircraft has 'the tendency'.
The worst-case scenario and why it is so important to follow the checklist is that after rotation, while
hands are still on the PLs and the aircraft is at TO power, you now take your hand off the PLs to retract
the gear. The aircraft is at full power and you have initiated the gear retraction. The left PM migrates to
idle, the right is at full power and AF does nothing for you. Full power on the right and a big huge brake
on the left side. What's next? Either a rapid recovery by simply moving the PL back forward and
tightening up the FL or what we have seen way to much of, airspeed decays and then the quick left turn
towards the ground. The videos are painful to watch.
PRO TIP: When TO power is set, raise your hand slightly and feel if the PL moves. If they don’t,
your FLs are set properly.
Check out the videos of PLM below. Once you feel what
it can be like, you will find yourself checking the FL many times before you get to the runway, at runway
lineup, and maybe a time or two while in flight.
Author: Kevin Carson, King Air® Academy
Image: Flying Magazine
