I can weigh in on this...The Army promotes this concept, probably based on the same program that the FAA uses in respects to "no notice" checkrides. The Army has rules and regulations that permit and order Standardization and Instructor Pilots to conduct at least one "No Notice" oral or written examination annually or semi annually(I can't remember which) for each aviator. Some of the instructors take this as a literal duty to go and examine an aviator in every performance task in the training manual. DA Evaluation and Standards(DES) travel from unit to unit, some while in combat, and evaluate in this manner, although you obviously know they are coming, but the units instructors will usually reserve the knowledge of who is receiving checkrides until just a day prior to receiving them. Usually Joe New PC guy will be evaluated. These evaluations are used in many ways, to motivate, to get aviators to adjust their attitude, get on the right track, to correct a negative action or bad habit. I've seen them in all the attack units I've been in. An example of a positve motivator is that a pilot has worked very hard in the unit and is a squared away aviator, he is given a flight with an instructor listed as a familiarization flight, and at the end, if successful, is informed that the flight was a "no notice" Pilot in Command evaluation and that he is now a PC. If he fails, then it was recognized as a familiarization flight and no negative entries are put in his flight records. An example to the negative side, if a pilot continuously ignores written publications and checklists, then he gets the hose. When he shows up to work he is taken to the table and instructed to get all his pubs and flight gear, goes through a full oral evaluation, full flight evaluation, and usually at the end of the flight, unless he is totally squared away, he is written up as Readiness Level 3, and recommended for retraining and further evaluation once training is completed.