Bridge Inspection Drone Pilots

Drone bridge inspections reach soffits, piers and bearings that are difficult and costly to access by traditional means. The imagery supports condition reports, defect tracking and maintenance planning. Flights around structures and over water are planned in advance and flown to that plan.

What this service involves

A drone inspection of a bridge photographs the structure at close range from positions that would otherwise need access equipment: soffits and the undersides of decks, pier faces, bearings, parapets, cable anchorages, abutments and the waterline. The output is imagery, and where the flight is planned for it, a measured three dimensional record that can be compared against the next one.

Where it sits in the inspection regime matters more than what the camera can resolve, and it is worth establishing before commissioning anything. Bridges are inspected to a published regime set by whoever owns the network. In Britain, the Design Manual for Roads and Bridges standard CS 450 sets general inspections at intervals of 24 months and principal inspections at intervals of 72 months, and defines a principal inspection as a close examination, within touching distance, of all accessible parts of the structure. In the United States, the National Bridge Inspection Standards require routine inspection at intervals not exceeding 24 months, with longer intervals available only through the risk assessment methods that regulation sets out.

CS 450 addresses remote inspection directly rather than leaving it to be inferred. Alternative means of access and inspection may supplement a principal inspection but may not replace it, and should not be proposed as a replacement for close up inspection unless doing so eliminates a significant safety hazard. On a structure covered by that standard, an aerial survey is therefore commissioned alongside the regime, or between inspections, or to work out what access the next principal inspection will need. It is not the principal inspection.

Who hires drone pilots for this, and why

Bridge owners and highway authorities needing a current record between scheduled inspections, or straight after an impact, a flood or a reported defect.

Consulting engineers scoping a principal inspection, who need to know what access will be required before pricing scaffold, a platform or a rope team.

Asset teams responsible for structures over water, rail or live carriageway, where putting a person within reach of the surface means a possession, a closure or a boat.

Insurers and loss adjusters after a strike or a scour event, where the date and the completeness of the imagery matter as much as its resolution.

Owners of structures outside any statutory regime at all: footbridges, estate and farm bridges, private crossings and disused structures, where nobody is inspecting on a cycle and the question is simply what condition it is in.

What to expect on the day

Access is both the reason for the job and its main constraint. Underneath a deck, satellite positioning is degraded or absent and the aircraft is close to steelwork, so the flying is done on other sensors and on what the pilot can see. Over water there is no straightforward place to put the aircraft down. Over a live carriageway or an operational railway, permission from whoever controls that asset is a separate arrangement from the aviation permissions and usually takes longer to obtain. Expect the plan to be built around those three things.

What the imagery records is the surface. Cracking, spalling, corrosion and section loss, coating breakdown, displaced bearings, blocked drainage, debris at the piers and scour at the waterline are all visible. What sits behind or within the material is not: delamination, internal corrosion, the condition of an embedded connection and the state of post tensioning are found by contact methods and by testing, which is why the standards treat close examination as the thing that cannot be replaced.

Deliverables are normally located high resolution stills organised by element, and increasingly a measured model where the same visit is flown with the overlap that photogrammetry needs, so that a defect can be found again in the same place next time. A report interpreting any of it is a separate instruction to somebody qualified to inspect that class of structure.

Bridge Inspection: frequently asked questions

Can a drone survey replace a bridge inspection?

Not a principal inspection, under the British standard for highway structures, which defines it as a close examination within touching distance and states that alternative means of access may supplement it but may not replace it. Structures outside a statutory regime are a different question. Establishing which regime applies to yours is the first thing worth doing.

Does the road or the railway have to close?

Usually not for the flight itself, and avoiding a closure is often the reason the work is commissioned. Flying over or beside a live carriageway or track brings obligations under the aviation rules that apply there, and separately requires the agreement of the organisation that controls the asset. The second of those is normally the one that sets the date.

Does it work underneath the deck?

That is the difficult part of the job rather than a detail of it. Satellite positioning is unreliable or unavailable under a deck, the structure interferes with the compass, and the aircraft is operating in a confined space near steel. It is done routinely by operators equipped and practised for it, and it is worth asking about specifically rather than assuming it is included.

How close can the aircraft get to the structure?

Close enough to resolve the surface detail an engineer works to. The limit is set by turbulence around the structure, by how well the aircraft can hold position where satellite positioning is degraded, and by what is safe near the members, rather than by the camera.

Can the same flight produce measurements, or only photographs?

Either, and the difference is decided before the flight rather than afterwards. Flown for measurement, with planned overlap and control, one visit produces a model that the next visit can be compared against, which is what turns a set of inspections into a record of change.

Drone pilots offering Bridge Inspection