On Friday, October 4, 2019 at 4:23:24 PM UTC-7, jp wrote:
Is it legal for non-CFIs to instruct others to fly?

The answer is, it depends on the level of training and whether the "student" needs to log instruction:

(all answers are for the USA)

1. If a pilot is rated and wants to get "instruction" in cross country, or another aspect of soaring, then the "instructor" does not need to be rated, and the "student" simply logs PIC time.

2. If there is a regulatory requirement to log training time, then most times the one providing instruction must be a CFI.

3. If the one receiving loggable instruction is not able to act as PIC (out of currency or not rated) then the instructor must be a CFI.

4. If a student rated pilot has another person in the glider, that person can only be a CFI. Anyone else would constitute a passenger that is prohibited for the Student Pilot.

Mike B. (CFI, CFII, MEI, CFI-G and former DPE for all of that)