The Federal Aviation Administration has apparently granted Amazon permission to test a newer variant of its parcel-delivering unmanned air vehicle prototype, following the award of an experimental airworthiness certificate for an out-of-date model.

The FAA announced in March that it had granted the online retailer permission to test its much-touted Prime Air UAV prototype, but this was met with disdain from Amazon when it announced some days later that the authorised aircraft was obsolete as a result of the lengthy process from the point at which it requested permission to the point at which it was granted.

However, it appears that testing of the newer prototype has been granted permission, according to a letter addressed to Paul Misener, vice-president of global public policy at Amazon, and the representative that filed the original certificate request in 2014. Misener also observed after the March authorisation was granted that it was for the wrong model.

Although the 8 April letter from John Duncan, the director of flight standards safety at the FAA, does not refer to Misener’s acknowledgement that the certificate was obsolete, the point at which it was written suggests the updated model has been considered in the granting of the permission.

Amazon drone - Rex Features

Rex Features

“This letter is to inform you that we have granted your request for exemption,” it reads. “The [unmanned air system] proposed by the petitioner is an Amazon-manufactured multirotor small UAS that has been described to the FAA in a confidential filing.

“I find that a grant of exemption is in the public interest.”

The UAV cannot operate at speeds exceeding 87kt (161km/h) and cannot surpass altitudes of 400ft. It must also be operated within line of sight of the operator who must hold a pilot certificate. The FAA certificate expires on 30 April 2017.