If you were giving instruction outside of 135/121 then according to the FAA Chief Counsel you are in violation of the FARs. The Creech letter is very specific about ATPs not being able to instruct outside the scope of part 135 and 121. If this is the case (you were using your ATP to teach under part 91), I advise you to delete your previous post and ask the moderator to delete my quote as you do not want such things on the internet. In addition anyone you have taught using your ATP under 91 can be subject to a 709 ride.
"Question 1. What is the intent of the 61. 167(b)?
Answer 1. Section 61.167(b) authorizes an ATP, who does not hold a flight instructor certificate, to give flight instruction only if the ATP and pilot are engaged in air transportation service. The authorization is limited in scope.
Question 2. Maya pilot who holds an ATP certificate and a BE-300 'type rating give dual instruction in a BE-300 aircraft to a commercial multiengine pilot with an instrument rating in "air transport service," if the ATP does not have a CFI and the flight is to be conducted under part 91 operating rules? If so, could this time count towards the 1500 hour total time requirement for the commercial pilot to obtain an ATP certificate?
Answer 2. We spoke to you by phone and confirmed that the flight described in your question is not part of an FAA approved air carrier training program approved under part 121 or part 135. Since the flight is not part of an FAA air carrier training program approved under part 121 or part 135, that fact is' dispositive of whether the ATP, who does not have a CFI, may give flight instruction,
While section 61.167(b)(2) authorizes an ATP to give instruction when the ATP does not hold a CFI, the ATP would have to comply with both §61.167(b)(2) and §61.3(d)(3)(ii). According to §61.3(d)(3)(ii), the instruction must be "... conducted in accordance with an approved air carrier training program approved under part 121 or part 135 .... " In your questions, the ATP is not a CFI and the flight is not part of an FAA approved air carrier training program approved under part 121 or part 135. As a result, the ATP may not instruct the commercial pilot. Since the ATP is not authorized to provide dual instruction, the flight time may not be counted as instructional time."