Last month it emerged that the Federal Aviation Administration (FAA) had granted Amazon permission to begin testing a delivery drone prototype for its Prime Air service, a venture that aims to transport packages to Amazon customers in under 30 minutes. But there was a hitch, with the company since revealing the vehicle cleared for use had already become obsolete. Things are now back on track with the FAA giving Amazon the green light to put its current models to the test.

Amazon first took steps to win the blessing of the authorities in July last year, when it petitioned the FAA for permission to begin testing its drones. But the agency's response was hardly swift, finally granting an "experimental airworthiness certificate" to Amazon in March 2015. The slow progress partnered with the now-evident worthlessness of the permit prompted Amazon to carry out testing of its more sophisticated models abroad, namely at a secret Canadian site only 2,000 ft (610 m) from the US border.

By way of a letter to Paul Misener, Amazon's vice president of Global Public Policy, on Wednesday April 8, the FAA has granted the company's request for exemption. This will clear the way for Amazon to begin testing its drones outdoors in the United States.

The exemption dictates that Amazon's drones fly no higher than 400 ft (122 m), no faster than 100 mph (161 km/h) and remain within the pilot's line of sight, among a raft of other conditions relating to safety and maintenance. These rules are consistent with a set of proposed guidelines around commercial drone flight that the FAA floated earlier in the year.

While it marks another step toward the realization of Amazon's ambitious drone delivery plan, there's still a long way to go before quadcopters are dropping parcels in your front yard.

The most obvious obstacle Amazon faces is convincing the FAA that drones can be safely flown beyond the line of sight. Well, that or it resorts to delivering packages only to buildings and people within a few hundred meters of its warehouses.

Ultimately, Amazon hopes to operate in a slice of airspace above 200 ft (61 m) and beneath 500 ft (152 m), where general aviation begins. It plans to fly drones weighing a maximum of 55 lb (25 kg) within a 10 mi (16 km) radius of its warehouses, at speeds of up to 50 mph (80.5 km/h) with packages weighing up to 5 lb (2.26 kg) in tow.

Editor's note: This article was amended on May 5th to correct an earlier error regarding the carrying capacity of the drones. We apologize to Amazon and readers for the error.

Source: FAA