Inactive Airplane Pilot Transitions to Gliders

Issue: Unfortunately, since Carl hasn't been flying airplanes in the last ten years, he never had a 61.56 flight review.   61.56(c) clearly states that in order for Carl to solo, and therefore be a pilot in command, needs to complete a flight review. The FAA also made a legal interpretation to this effect in 2016, called the Beard Interpretation. Prior to the Beard interpretation, it was colloquially interpreted that Carl was a student pilot, and therefore wasn't subject to the flight review because of 61.56(g)  However, the Beard interpretation reinforces that Carl is a private pilot, not a student pilot, and that a 61.87(a) solo endorsement for student solo is not appropriate. For those who are curious: the appropriate endorsement is 61.31(d)(2).

Here is a decision flowchart to help with Carl's situation: 

Solution #1: Surrender Pilot Certificate

Carl can surrender his private pilot ASEL certificate, then re-apply for a student pilot certificate.
Advantage: It works but it's dumb. Don't do it. It's so dumb we didn't include it in the flowchart above. 
Disadvantage: Carl will have to take the FAA knowledge test for gliders. He would not have to if he retained his ASEL pilot certificate.  If Carl ever decided to fly airplanes again, he would have to repeat the whole ASEL training program, including FAA knowledge tests, and FAA practical tests in order to regain any ASEL ratings. 

Solution #2: Flight Review in Airplanes

Carl has to "bite the bullet" and go complete a 61.56 flight review in airplanes, even if he doesn't want to fly airplanes again.
Advantage: After successfully completing the 61.56 flight review, it will allow Carl to go fly airplanes again, and would be able to solo a glider, after all of those endorsement requirements are met. 
Disadvantage: Theoretically, Carl wouldn't need to have his medical certificate re-issued, but the instructor may insist on it.  It is a significant expense to go get a flight review to return to flying status after 10+ years, and that is a cost Carl would have to absorb, without adding specific relevance to flying gliders. 

Solution #3: WINGS Training in an Airplane

Carl has to "bite the bullet" and go get FAA Wings training in an airplane, even though he doesn't want to fly airplanes again.
Advantage: after completing a phase of WINGS training, Carl can immediately fly airplanes again, and would be able to solo a glider, after all of those glider solo endorsement requirements are met.
Disadvantage: Much like Solution #2 above, it's significant expense for Carl to get up to flying skills necessary for each of the ASEL WINGS credits that the CFI-A is willing to give out. 

Solution #4: WINGS Training in a Glider

Complete FAA WINGS flight training in a glider. Have the CFI-G endorse Carl for the FAA WINGS activity named "APT-Glider Student Activity" Note at the top of this WINGS course, it clearly states, "This Accredited Activity is available to all airmen." Also note that this WINGS activity has all of the knowledge and flying credits needed to complete the basic phase of WINGS. This means that after successful completion, Carl can use this FAA WINGS credit to become compliant with 61.56(e). It also means that Carl can do this flight activity in a glider, despite not having a glider pilot certificate.  

There is often confusion about this scenario.  Many instructors incorrectly conflate completing WINGS activity with 61.56(c)(1), which states that a flight review must be accomplished in a category, class and type in which the pilot is rated. Remember, completing a phase of an FAA sponsored proficiency program (WINGS in this case, as described in 61.56(e)), makes a pilot exempt from having to perform the flight review in 61.56(c). Carl didn't complete a flight review in a glider, Carl completed a phase of the WINGS training. He completed activity explicitly indicated that it is available to all airmen.  

Advantage: Carl doesn't have to get a 61.56 flight review in airplanes. After completing the WINGS training and his glider solo endorsement, Carl will be able to solo gliders. All of that training Carl did to prepare him for his first solo in gliders is pretty much what's required to complete the "APT-Glider Student Activity" WINGS program, so there's no unnecessary duplication.
Disadvantage: Beyond the difficulty of logging into WINGS and finding the right credit to give, there really isn't any disadvantage. 

Important Caveat: the instructor issuing WINGS credit should note that immediately following the completion of the WINGS activity, Carl could legally go for a solo in his old Bonanza.  In Carl's case, a flight review or a completion of a phase of WINGS activity is all that's needed to go fly an airplane if the pilot has an ASEL rating. There's no such thing as a 61.56 flight review in gliders, then another 61.56 flight review in airplanes.  One flight review per 24 calendar months is all that is needed to exercise any part of an airman certificate. The recommending instructor should have a conversation with Carl to let Carl know that just hopping in a Bonanza after getting WINGS credit in a glider would be reckless.