Asymmetric Reverse Leads to King Air Excursion

[skybluetrek]

Without reading the report, that sounds like a ground prop solenoid issue. In the 300 and 350 there is actually an annunciator light to warn you of this as it's seen as quite serious. The issue isn't just that there is a mismatch in torque in reverse, but that one prop stays at the flight idle low pitch stop and the other one potentially one either goes into the ground idle (beta) or even full reverse mode. The 1900 has basically the identical electric low pitch stops as the 300/350 but for some reason that light and any mention of it is not in the AFM. It might just be the longer wheel base and bigger rudder of the 1900 makes it less of an issue.

Shitty reverse rigging is one of my biggest pet peeves from my time in Beechcraft. Engineers hate messing with it because every little change requires a full engine run, so any adjustments cause hours and hours of fuss. One 200 I flew actually had no reverse thrust at all and had presumably been like that for years. I can still hear the room full of engineer eyes rolling when I told them. The N1 never even increased with the levers at the stops, just beta. When they finally finished messing with it you could parallel park that Beech.

Correct me if I'm wrong but in case you didn't see the light or it was too late to pull the CB and you land, when you lift the levers over the gate, both props will go from flight idle to ground fine and into reverse if needed. A ground prop solenoid issue is not directly related to a mismatching/rigging reverse problem.

With the failure of the ground prop solenoid, one or both props stay at the flight idle low pitch stop. So if you were to apply "full beta" on both levers you'd have a massive difference in blade angle making control difficult or even impossible on a low friction runway. Whereas yes you are correct that if you lifted the levers over the gates and apply full reverse, the squat switch is bypassed and both props "should" go into reverse.

I believe several early 300s were written off because of this and it was an AD that required the addition of the ground prop solenoid light. I could be totally wrong, but when i see uneven reverse sends 300 or 350 off into the weeds it's a red flag to me.

Personally I started doing a full reverse check on the runup of all Beech aircraft I few for this reason. A lot of guys are afraid of reverse, you just have to be very careful where you do this runup, watch your oil temp carefully when doing it, you just need 5 seconds to get to know your engines. If your'e really not sure, ask the engineer to come with you. They do prolonged reverse runs (or they should).

I know where you're coming from but that is not quite correct. The ground prop solenoid is a serious issue if energized in flight, and if you land in that condition, the two seconds after touchdown might cause asymmetrical problems if you leave the levers at idle as one prop may go to the ground low pitch stop and the other one stay at the flight low pitch stop. After that and with weight on wheels the system is energized anyways, allowing both props to continue to the ground low pitch. But even in that scenario, if you promptly bring the levers over the first gate to ground fine, it doesn't matter anymore, the beta valve will now allow both props to continue to -2° and onwards regardless.

[pelmet]

Hmmm……have heard of ground fine but not on a King Air.

Found this interesting article about the newer versions, which I never flew………
https://kingairmagazine.com/article/the ... rs-do-not/

Bottom line………certification stuff for bigger models and parts commonality on smaller models once it started being used on larger models.

[co-joe]

Hmmm……had heard of ground fine but not on a King Air.

Found this interesting article about the newer versions, which I never flew………
https://kingairmagazine.com/article/the ... rs-do-not/

Bottom line………certification stuff for bigger models and parts commonality on smaller models once it started being used on larger models.

Thanks for the clarification Skybluetrek, much appreciated.


That's a great article Pelmet. I did a full 350 course with Simuflite in DFW and don't ever remember them covering rudder boost and its effect on an RTO, of all the companies I flew 200s for, most did on wing training (although I have been to both Simuflite and Flightsafety for the 200 as well). Only one company taught full reverse on single engine landings/ RTOs. The rest briefed it as an option but never actually did it (and in the sim it was a non event).

The discussion on raising the flaps on landing is an interesting one. I remember at Borek they specifically forbid this practice because the gear and flap handles on the 100 and 200 were on opposite sides of the panel and the fear was that someone (who was dual typed) would retract the gear by accident under stress before there was enough weight on the squat switch to prevent it.

Here's my favourite quote from the article.

A PT6 powerplant mechanic who can correctly make all of this happen as it should, while matching left and right power levers together, is worth his or her weight in gold and can be somewhat hard to find! This is what engine “rigging” is all about and it can be a frustrating and time-consuming experience when done by a less-experienced and less-knowledgeable person.

I always brought beer whenever I planned to write up a PT6 rigging snag in the log book, because by the end of the shift, I knew the engineers would be thirsty.

[‘Bob’]

The ground fine gate is fine… but still academic because of the pain to rig.

So it’s pretty easy.. as you taxi out you pull back and make sure you hear the blades go into beta but the engine doesn’t spool. That’s your beta range and good enough to land with even when the runway is 1/1/1 at most airports if winds are light because directional control is far more important than distance.

If it’s ineffective you have to pull back further.. even over the reverse gate in some cases for planes with GF gate. Also pay attention to the split and/or stubborn solenoids if there is one. Just because the solenoid is energized doesn’t mean it’s doing what it’s supposed to be. Prop RPM and/or prop pitch lights as applicable (prop pitch is a blade position indicator.. not a system status indicator).

And if you pull further back and it’s screaming without the effects of reverse.. or bogging down while the blades bite but there’s no N1.. dead bands are off. N1 should be at selected idle through the entire beta range (preferably low idle).

Bottom line. Just pull back to get the blades fine (beta), but not have the engine spool (reverse).. and most of your asymmetric thrust/drag, blade erosion, terrified passenger problems will disappear and you’ll still stop in time.

[KAG]

Bob, I'm not a self proclaimed expert in anything, especially somthing I haven't touched since 2006.
That said there's no reason why you can't use reserve thrust on gravel, none. I never said it's required, I said you can. I've have taken king airs into short, Iced up runways (2400" being the shortest) and i absolutely used reverse thrust. It's not an ego thing, sometimes it's actually required.
Also, since experience is lessening it's not not a bad idea to pass along a few pointers.

[Old fella]

Bob, I'm not a self proclaimed expert in anything, especially somthing I haven't touched since 2006.
That said there's no reason why you can't use reserve thrust on gravel, none. I never said it's required, I said you can. I've have taken king airs into short, Iced up runways (2400" being the shortest) and i absolutely used reverse thrust. It's not an ego thing, sometimes it's actually required.
Also, since experience is lessening it's not not a bad idea to pass along a few pointers.

Agreed. Sounds like we both have a shared background(King Air) .

[Mick G]

Bob, I'm not a self proclaimed expert in anything, especially somthing I haven't touched since 2006.
That said there's no reason why you can't use reserve thrust on gravel, none. I never said it's required, I said you can. I've have taken king airs into short, Iced up runways (2400" being the shortest) and i absolutely used reverse thrust. It's not an ego thing, sometimes it's actually required.
Also, since experience is lessening it's not not a bad idea to pass along a few pointers.

I agree Bob. In havent touched a king air in 45 years, but all is relevant and it's the way they are gravel or not

[J31]

Bob, I'm not a self proclaimed expert in anything, especially somthing I haven't touched since 2006.
That said there's no reason why you can't use reserve thrust on gravel, none. I never said it's required, I said you can. I've have taken king airs into short, Iced up runways (2400" being the shortest) and i absolutely used reverse thrust. It's not an ego thing, sometimes it's actually required.
Also, since experience is lessening it's not not a bad idea to pass along a few pointers.

I agree Bob. In havent touched a king air in 45 years, but all is relevant and it's the way they are gravel or not

There were Beech King Airs WAY back then! Sorry Mick G, I just had to give you a good natured nudge!