North Carolina DOT gets Waiver to Fly Drones Beyond Visual Line of Sight for Bridge Inspections

According to the 2017 infrastructure report card, the U.S. has 614,387 bridges. four in 10 of which are 50 years or older. 56,000 of the nation’s bridges were structurally deficient in 2016, and on average there are 188 million trips across structurally deficient bridges each day. Improvements in inspection methodologies are vital to ensure public safety. The latest in those is the North Carolina Department of Transportation’s (NCDOT) waiver to use drones for bridge inspections Beyond Visual Line of Sight (BVLOS). In this blog, you’ll read an interview we had with Ben Spain. He is serving as the NCDOT UAS Program Manager.

Picture courtesy of Skydio

Q: What exactly is the BVLOS waiver?

NCDOT can now use drones to examine the underside of bridges Beyond Visual Line of Sight (BVLOS) without visual observers and tracking antennas. NCDOT, a lead participant in the Integration Pilot Program (IPP), was granted the waiver by the Federal Aviation Administration (FAA).

The waiver however stipulates that the drone should always be within 50 feet of the bridge. While this is a restriction, this stipulation made it easier for NCDOT to get the waiver as there is no manned aircraft in this area and therefore is considered as a very low risk airspace.

Another stipulation is that the bridge can’t be higher from the bottom of the deck, than 100 feet, to eliminate the risk of encountering manned aircraft. As a matter of fact, in the middle of their waiver process an airplane was flown in Michigan under a bridge that was approximately 150-175 feet tall.

Q: How much time did it take you to get the waiver?

It took around 4 months. The waiver process was started in June 2020 and was approved in September.

Q: How will drones be used to inspect bridges in North Carolina?

Drones will be used as a fast assessment tool for potential damages and thorough examination of specific defects. They are considered as “digital binoculars”.

Drones will not, for now, replace traditional methods for the Federal Highway Administration (FHWA) inspections.

As for the actual drone operation, it will depend on the flight objective as well as the bridge in question. At the very basic level, a single pilot can fly, capture pictures and come back to the office to analyze and document them. The flying for now is manual and no 3D modeling is being used yet.

Moving forward the drone’s live feed will be streamed where an engineer examines the footage and takes pictures of problem areas.

Picture courtesy of Skydio

Q: Will drones replace certified bridge engineers in the field?

Drones will not replace certified bridge engineers in the field as the FHWA still requires this.

Q: Will the drones be used on all the 13,500 NCDOT bridges?

Most bridges can be flown without losing visual line of sight with the drone.  The waiver will be used for those bridges where VLOS cannot be easily maintained, such as on some of the longer coastal bridges.  

There will be a challenge operating drones on the underside of bridges that go over roads and highways (as opposed to over water) as another waiver would be needed in that case. Otherwise, the road and highway in question would need to be closed which would require lots of efforts and approvals.

Nevertheless, there are plans to expand drone operations to be able to fly over cars and people by applying for a waiver to fly over people and moving traffic.  One way to achieve that would be to add a parachute to the drone.

Q: What about the drone’s short flight time challenge?

Drones will not be used for the full inspection of the bridge; they are there to aid and so will be used only when necessary. Therefore, there won’t be a need for long flight times at this moment. In case they are needed, back-up batteries are available in the field to keep the drones flying.

Q: Who will do the flying and how?

The Special Inspections Unit under the Structures Management Unit at NCDOT will handle the flying at first. As for NCDOT contractors, they are expected to handle the flying part and ensure compliance.

Q: When can we expect drone bridge inspections in North Carolina?

We are currently training our first group of pilots for the waiver. We should start seeing the drones in action as early as the 1st quarter of 2021.

Picture courtesy of Skydio

Q: Why should agencies adopt drones and what’s your advice?

The time and cost saving with drones is huge. For instance, drones can reduce the number of expensive snooper trucks needed.

Agencies should hire drone experts with their full-time job being the safe integration of drones. Ben mentioned that he is not a bridge inspection expert himself however he knows all about the FAA and regulations. He is bridging the gap between the various needs of NCDOT teams and the safe and proper integration of drones within the organization.

Ben also advises agencies not to focus so much on the monetary return at first and to be careful with marketing hype around the drone industry.

In conclusion, expanding the usage of drones in the bridge inspection industry is a great step towards ensuring the safety of bridges and the public. We are still scratching the surface when it comes to the advantages of this technology. For instance, drones can be equipped with multiple sensors such as thermal and LiDAR and others that could help engineers collect a huge array of bridge data. This will drastically improve the accuracy of bridge inspection and maintenance. As advancements are made, check back for future blog posts to learn more about what is available!


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