Differences training is additional training to another variant
After completing the type rating training, the privileges of your type rating are limited to the specific variant on which the skill test with the TRE examiner was completed. For example, if you have completed initial type rating training on a Boeing 737 and a skill test with TRE on a Boeing 737 Classic generation, your privileges are limited to the Boeing 737 Classic only. Logically, you can't fly the Boeing 737 NG without additional practical training and possible checking with the TRE B737.
With the Cessna 525, the situation is even more complex. For example, if you have passed the skill test with TRE C525 on C525A - CJ2, your privileges are limited to CJ2. In this case, additional training with the TRI C525 is required to fly the Cessna 525B - CJ3.
The additional training with TRI C525 that is called differences training.. The need for differences training is established in AMC2 ORA.ATO.125 (b)(2) for the type trainings. In addition, differences training is also required by AMC1 FCL.700(b) and FCL.710 with GM1 FCL.710(a).
Part-FCL explicitly states that when differences training is required, additional knowledge and flight training is required in either the aircraft or FSTD (simulator) representing particular aircraft variant.
For this reason, differences training is required when transition is done to the different generation or aircraft variant than the one used for the skill test with TRE examiner. Differences training is therefore a mandatory requirement for flying another variant of the aircraft, even though the differences training is not endorsed in the pilot's license. The completion of the differences training is recorded either in the pilot's logbook or stored by an operator (airline).
Examples when differences training is mandatory:
- transition from Boeing 737-400 to Boeing 737-800
- transition from Cessna 525 CJ3 to Cessna 525 CJ4
- transition from Bombardier CRJ 200 to Bombardier CRJ900
Examples when differences training is not required:
- transition from Boeing 737-400 to Boeing 737-300
- transition from Cessna 525 CJ2 to Cessna 525 CJ2+
- transition from Bombardier CRJ 900 to Bombardier CRJ700