Experimental Aircraft Operating Limits

Experimental Aircraft Operating Limits:

Phase I verses Phase II Operation

There is a lot of confusion regarding the concept of experimental aircraft operation . I will attempt to clear this up . Basically, Phase I operation is the state the aircraft is in when you are conducting flight testing of your aircraft . Phase II operation is after you have determined the “aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation . ” In fact, that is the exact wording in your Experimental Aircraft operating limitations . So how do we use this opportunity?
The FAA considers an Experimental Aircraft, whether amateur built or light sport, your experiment . As such you may pretty much make the modifications you want to it as long as it is tested and found safe to operate . (And meets the definition of a Light Sport Aircraft if it is ELSA) . The aircraft operating limitations provide for you to take your aircraft into and out of a flight testing regime any time you make a major change to that aircraft . So, what constitutes a major change? This would be any modification that will change the previously tested flight characteristics of the aircraft . It may take the form of a different engine, different wing, or a modification to the airframe and a different propeller .
For instance if you certified your aircraft with a Rotax 582 and now decide to install a Rotax 912 engine . The new engine will weigh more and have more horsepower . Consequently it will change the CG, how the aircraft performs and would be considered a major change . The proper procedure, after the work is completed, would be to enter the modification in the airframe logbook, then make an entry stating the aircraft is in phase I operation . Here is an example:

8/25/2008 TT 250 hr .

Removed Rotax 582 ser# 1234567 from airframe and installed Rotax 912 Ser#9876543 .
Aircraft in phase I operation .

Signed ____Joe Aviator__

Remember anyone may work on, modify and maintain an experimental aircraft . There is no certification required for that . The only requirements are that the entry in the logbook have the date, total aircraft time, work performed, who did the work and the signature of the person performing the work (which constitutes the ok for return to service) . Next you should plan a flight test program for your modification . You will want to include both minimum weight flights and flights at the maximum gross weight you intend to operate . For instance, if you want your maximum gross takeoff weight to be 955 lbs you must ballast additional weight in the passenger seat to achieve that weight . You may not use a passenger as that additional ballast . All phase I flight testing must be done with the pilot as the sole occupant of the aircraft . When you sign the aircraft back into phase II operation you will be stating the maximum weight and speeds you tested and also the minimum speed tested . Additionally, all flight testing must be done within the flight test area prescribed in your operating limitations, during VFR conditions, over an sparsely populated area and out of congested airways .

Your test program will include all maneuvers such as climbs, descents and turns and any other maneuvers you deem necessary to test to assure safe operation in all flight regimes . This testing should be a minimum of 5 hours or the required hours listed in your operating limitations . Notice I said minimum . If you find some problems during the flight testing you may have to make additional modifications and do further testing to be able to certify the aircraft is safe. After successful completion of the required flight test hours and if you find no adverse flight characteristics you may now make an entry in your airframe logbook changing the aircraft into phase II operation . An example would be:

9/3/2008 TT 255

I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation . The flight test was completed under the following conditions: maximum operating weight 955lbs, Northwing Quest GT-4 wing, maximum demonstrated airspeed 80 MPH, and minimum demonstrated stall speed: 20 MPH .
Aircraft in phase II operation .

Signed____Joe Aviator___

Now you may again take passengers in the second seat of your aircraft . There is no limit to the amount of modifications, the extent of the modifications or the amount of times you may go from phase II to phase I and back . The thing to remember is, this aircraft is your experiment and you may experiment with it to your hearts content, … as long as it is properly tested .