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