Date: 201211
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Taxi
ATC / advisory: CTAF ZZZ
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Multiengine
Human factors: Human-Machine Interface
Anomaly: Ground Excursion Taxiway; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Became Reoriented
Contributing factors: Aircraft; Airport; Human Factors
Primary problem: Human Factors

Narrative: My experimental aircraft has a tricycle landing gear; castering nose wheel; and heel brakes. Taxiing at low speed requires differential braking. On most taxiways; taxiing at ground speed of greater than 12 KTS gives adequate rudder authority. However; this taxiway required dragging one brake rather heavily. In this incident; the nose started swinging to the left and the speed was too low for much help from the rudder. I applied full right rudder and a short throttle burst; which often is sufficient to straighten the aircraft out. In this case; it was not; so I applied brakes. Due to the rudder deflection; my right foot didn't completely engage the right heel brake; but the left foot was fully on the left brake pedal. The result was that the nose swung to the left; placing me about 45 degrees to the taxiway and only about 10 FT from the edge. Once differential braking is applied; it typically takes a few seconds to get the nose wheel turned; so it did not appear that I had room to straighten the plane out and continue taxiing. Instead; I elected to arrest the rotation and continue straight ahead off into the grass as there were no obstructions straight ahead. I also shut the engine down as quickly as I could to prevent a prop strike. The engine stopped just after I left the asphalt and I was able to come to a stop about 15 FT off the taxiway. I exited the aircraft and turned it around by depressing the tail. An airport official immediately came to my aid and after obtaining my name and phone number; he assisted me in pulling the aircraft back onto the taxiway. I performed a careful inspection of the landing gear and propeller and noted no damage. In particular; there was no evidence of any contact of the propeller with the ground or grass.There are two lessons to be learned:1. Throttle bursts to straighten out during taxi; at least in my aircraft; are not a good idea. While they usually do work; they don't always work; and if they don't; there is little time to fix things; even as slow as I taxi.2. My taxi technique needs to be revised so that I don't remove my heel from the brake pedal. Full rudder deflection is possible with my heel on the brake pedal; but it's not too comfortable. As a result; it's tempting to lift the heel. Clearly; that is not a good idea.




Synopsis: Experimental aircraft pilot reports loss of control during taxi resulting in a taxiway excursion. Heel brakes were cited as a factor in the incident.