Which form is used to change an authorization on an allowance source code?

The correct choice for changing an authorization on an allowance source code is AF Form 601. This form, known as the "Equipment Authorization Change Request," is specifically designed to manage changes in authorization for items related to equipment allowances. It serves as a formal request to modify existing authorizations, which is essential in maintaining accurate records of what is authorized for use in various operations.

Using AF Form 601 ensures that proper procedures are followed when adjustments are needed regarding allowances. This maintains the integrity of inventory and assures that resources are allocated as required by the mission. Every request submitted through this form undergoes the necessary review and approval process, making it a critical component in the management of aircrew flight equipment.

The other forms listed serve different purposes: AF Form 254 is generally used for requesting a record review, AF Form 103 is utilized for documenting the transfer of property, and AF Form 990 is related to supply discrepancy reports.