Abstract In this paper, we propose a Kalman Trust Estimator (KATE) to check misbehaviour by the drones in Internet of Drones. Internet of Drones is a Flying Ad Hoc Networks connected to internet is a wireless mobile network of energy constrained devices deployed in a high multidimensional free space. This leads to small neighbourhoods and high temporal variation of drone density. IoD is characterized by drones possessed or controlled by different owners that form the network. A legitimate drone may be made to act selfishly to further interests of its owners or may be compromised to act so. This warrants establishment of trust in a drone to accept the veracity of the messages or sensed information sent by it. Earlier, several trust models have been proposed to achieve secure and reliable internode communications. They often detect drones as malicious by merging the previously formed direct and indirect trust values but do not consider the impact of old trust values on the current trust values. The trust values stored over the internet last for longer duration. Hence, for old transactions, they turn vague with time, especially when only sporadic interactions has occurred. KATE promotes the exchange of only correct messages with reduced delay. It simultaneously combines the direct and indirect trust values among the drones in two different contexts. It attaches the state transition variable and the importance factor to the direct and indirect trust values during trust estimation. Weighted fused decision values is used in decision-making based on the estimated trust values. Our simulations show the efficiency of KATE in terms of high decision accuracy in minimal rounds of trust estimation.