A Commercial Air Transport (CAT) operator is a company which holds an approval, granted by an authority. Such an operator will have their own staff, acting under their approval.

However, an operator may need to use another company to carry out work on their behalf (a contractor). For example, consider an airline who do not have their own staff at a remote base and so they may use a handling agent.

We have 2 situations to consider in these questions:

1. The contractor DOES NOT hold their own approval (from an authority). No problem, they can still carry out the task, but under the operator's approval.

2. The contractor DOES hold their own approval. Now the contractor can carry out the work under their own approval. But the operator must check that the contractor is doing things properly by checking for compliance monitoring, risk management, holds the correct approvals etc.

In either case, a written agreement is required between the operator and the contractor. A verbal agreement is insufficient and can't be verified by the authority. More information from the source material below...

EASA AIR OPS
ORO.GEN.205 Contracted activities

(a) When contracting or purchasing any services or products as a part of its activities, the operator shall ensure all of the following:

(1) that the contracted or purchased services or products comply with the applicable requirements;
(2) that any aviation safety hazards associated with contracted or purchased services or products are considered by the operator's management system.

(b) When the certified operator or the SPO authorisation holder contracts any part of its activity to an organisation that is not itself certified or authorised in accordance with this Part to carry out such activity, the contracted organisation shall work under the approval of the operator. The contracting organisation shall ensure that the competent authority is given access to the contracted organisation, to determine continued compliance with the applicable requirements