Every factory deviates sometimes. The difference between a good supplier and a bad one is whether you hear about it before the units ship or after.
A deviation is a documented, time-limited permission to build something that does not fully meet the released definition — a substitute component, an out-of-tolerance feature, a missing marking. It is a normal part of manufacturing. What is not normal is a deviation that nobody asked for.
The mechanics are simple. The supplier states what deviates, why, how many units are affected, what the technical assessment is and how long the permission should last. The customer approves, rejects or asks for containment. The approval travels with the affected serial numbers so that the units can be identified years later.
The hard part is culture, not paperwork. A supplier under delivery pressure is tempted to ship and hope, especially when the deviation looks harmless. Our position is that the customer owns the risk decision because the customer owns the product — and that a late delivery with a phone call beats an on-time delivery with a surprise.
Buyers can help by making deviation approval fast. If a request takes three weeks to answer, the incentive to ask disappears. A supplier who can get a decision in a day will ask every time; a supplier who cannot will eventually stop asking, and that is the moment quality escapes become someone else's problem in your plant.
— GANI Manufacturing engineering team