A broken accident chain!

[Vance]

I fly a narrow line between allowing the client to experience the consequences of their mistakes and preserving the aircraft in flying condition.

I am often surprised by the creative ways the aircraft is put in harm’s way.

Mishaps tend to be a chain of mistakes and the trick is to break the chain before becoming an accident report. I will call the primary student Bob to protect his anonymity.

I started Bob in the back seat because there is less to manage. After some successful flight experience (around eight hours of dual and many takeoffs and landings) I moved Bob to the front where he has to manage the magnetos for the magneto check, the rotor brake, the toe brakes for steering and the radio. I cannot see the engine instruments from the back. I have the basic flight instruments of altitude and indicated air speed in the back. There is a lot to see and often the client’s vision is already narrowed by learning to fly.

We had just filled up with fuel and are both well over two hundred ponds so we were flying near maximum takeoff weight (first link in the accident chain).

Bob had floated long on the landing so we were quite a ways down the 8,000 foot runway when Bob began his takeoff roll (second link).

Bob was slow to get to full throttle once the rotor began to accelerate using up more runway (third link).

Bob let the nose come up too far and lifted off early (about 25kts) well below the minimum power required speed so we weren’t going to climb very fast until he lowered the nose and built up some airspeed (forth link).

We flew over the end of the runway at about 50 feet above the ground and did not seem to be climbing despite being only slightly below minimum power required speed (46kts) (fifth link) and I took control in an attempt to break the chain.

I carefully lowered the nose for best rate of climb trying to break the accident chain and she still wasn’t climbing.

I asked Bob what the engine rpm was and it was 2,290. Anything below 2,300 rpm and the engine is not running correctly and the takeoff is supposed to be aborted (sixth link). Bob had not noticed the low engine RPM.

I was trying to diagnose the engine problem without engine instruments so I asked Bob if the fuel pressure light was on and what the various instruments read.

I felt we could lose all power at any moment so I continued to scan for landing spots. There was a nice dirt patch straight ahead that is crisscrossed with fences. As I turned left we were over some mature crops so it would be an interesting landing. There were a few dirt roads but they were littered with people and vehicles. There were several fences and lots of irrigation ditches.

I called the tower to let them know I had engines problems and would be returning and asked for runway two. They were in the process of launching an Aironca on runway three zero so I felt returning to runway three zero was not a viable option. The tower (ATC) was quick to respond runway two clear to land and canceled the Aironca’s takeoff clearance. There is a stand of eucalyptus trees that I needed to go around making very gentle turns. The landing was uneventful.

I had to remind Bob that he had the brakes and we did not cross runway three zero till I was sure the takeoff cancelation for the Aironca was successful.

Back at the hangar Bob worked his way down the shutdown list; rotor brake on below 100 rotor rpm, lights off, transponder off, radio off, intercom off, alternator off, lean cut off, mag switches on. Even with the intercom off; I could hear Bob’s expression of surprise and dismay as he discovered only one of the magneto switches was in the off (run) position.

We still haven’t figured out how Bob hit the switch or why he didn’t see the red light on the tachometer when a magneto is not working right. The magneto switches are well out of the way and off in the forward position so any bumping is likely to turn them off (run position).

I went for a solo maintenance flight and saw over 2,400 rpm on takeoff and saw just over 900 feet per minute of climb so I felt we had found the problem. I saw 2,650 rpm on down wind at around 90kts (103 mph) indicated air speed.

I checked the ATIS and winds were variable at 4kts. As we taxied down to the run up area on Alpha the new ATIS came out with winds 270 at 11kts gusting to 18kts. We both felt this was over Bob’s wind limit with his current level of experience so we headed back to the hangar and packed it up for the day.

Each of the links is not dangerous on its own but when linked together they may form an accident chan. With the help of ATC and some luck we were able to break the accident chain.

 

[eddie]

Your lucky you have a strong Lycoming engine, takeoffs on one mag usually don't turn out very well I would also say that your piloting skills are way above average
you did all of the right things,you kept your cool,and flew the aircraft,

 

[WaspAir]

Hi, Vance -
Did you declare an emergency when you called the tower?
Just wondering.
A typical tower response to declaring is "cleared to land, any runway", and they cancel all other clearances immediately.
J.R.

 

[Vance]

Your lucky you have a strong Lycoming engine, takeoffs on one mag usually don't turn out very well I would also say that your piloting skills are way above average
you did all of the right things,you kept your cool,and flew the aircraft,

Thank you Eddie, I was surprised at how much the small drop in rpm affected the climb out.

Bob probably could have handled it if I had talked him through it but I didn’t know how much worse things were going to get so I took control.

I feel fortunate ATC was so responsive so I did not have to declare an emergency.

It is amazing how long it takes to fly that short distance when at 50 feet agl and expecting the engine to go quiet at any moment.

I send my Bendix magnetos out every five hundred hours to be rebuilt. Typical rpm drop is 40 rpm with ten rpm difference between left and right.

 

[Vance]

Hi, Vance -
Did you declare an emergency when you called the tower?
Just wondering.
A typical tower response to declaring is "cleared to land, any runway", and they cancel all other clearances immediately.
J.R.

An excellent point J.R and good advice.

I have declared an emergency in the past when the engine did go quiet and that was their response; "Experimental Two Mike Golf all runways and taxiways clear to land."

I feel it is important to not hesitate to declare an emergency. If the tower had not responded as they did; I would have.

If I declare an emergency they immediately roll all the emergency equipment and shut down the airport for at least twenty minutes. There is also a lot of paperwork and I may not be able to move the aircraft till the FAA says it is OK.

I probably should have declared an emergency anyway.

 

[eddie]

Well not declaring an emergency go's to good aviation decision making,you were still flying although not climbing, you asessed the situation in an instant

and acted accordingly. That's what a good pilot does. You turned what could have been a disaster into a non event.

 

[magknight]

Seems with the current placement of the switches it would be easy to bump them into the off position. Maybe consider switch guards? So glad you recovered safely. These types of situations are always a lasting lesson learned!

 

[Vance]

Well not declaring an emergency go's to good aviation decision making,you were still flying although not climbing, you asessed the situation in an instant

and acted accordingly. That's what a good pilot does. You turned what could have been a disaster into a non event.

Thank you Eddie, it was a lucky guess and it was fortunate that ATC handled it the way they did.

My actual guess was that the engine would stop and I would not make it to the runway.

My advice in that situation would be to declare an emergency.

I did have places to land but they would have likely been hard on The Predator.

 

[Vance]

Seems with the current placement of the switches it would be easy to bump them into the off position. Maybe consider switch guards? So glad you recovered safely. These types of situations are always a lasting lesson learned!

Good observations Jason.

We tried to imagine tripping the switch to the on position and could not find how it was done.

Before I had the run position forward I did knock them on and killed a magneto a couple of times.

The throttle comes forward and the mixture remains back.

The transponder is close by but there is no need to fool with the transponder in the pattern.

This is the first time since I moved the switches that they have been inadvertently actuated in about 1,500 hours.

I doubt Bob will do it again and if he does he will remember what the red light on the tachometer means and correct it.

Because the magneto switches are my emergency way to stop the engine if the lean cutoff doesn’t work I don’t like the idea of guards that might slow down the response to a problem that may escalate quickly.

 

[Doug Riley]

Quite awhile ago, I was flying my Kolb FW ultralight (with a Rotax 447) on a X-C. I went fishing about beside me for a chart, and managed to switch off the engine! (I'd bought the plane used, and the builder had installed a toggle switch on the airframe down on the side of the seat, out of the pilot's straight-ahead view). The engine took long enough to spool down that there was time for me to switch it back on again before it stopped.

I put a big U-shaped guard on that switch when I got back. I'm a fan of switch guards.

 

[Chris Burgess]

Good read for those with mags.

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