What each one involves
Technician entry. The turbine is stopped and the blade locked. The blade is a confined space, so the entry needs at least two people, a rescue plan, atmosphere monitoring and the permits the site requires. The technician enters through the root hatch with a camera and a lamp, moves along the blade until the section becomes too narrow, photographs what is seen, and comes back. The blade is then unlocked, the next blade rotated into position, and the sequence repeated.
Crawler. The turbine is stopped and the blade locked in the same way. The operator lifts the crawler into the root, clips on the pull-out cable, and drives it from a tablet that joins the crawler's own wireless link. The crawler records as it goes and drives back, or is pulled back on the cable. Nobody enters the blade. Detectra weighs 3.7 kg and travels in two cases; the whole kit is hand-carried up the tower.
Coverage
This is the decisive difference. A technician's inspection ends where the blade becomes too narrow to move on, a short way past the root. Everything beyond that point, which is most of the blade and includes the part of the trailing-edge bond under the highest strain, is not inspected. Detectra drives up to 80 % of the blade length from the root.
Put differently: a technician inspects the root zone thoroughly and the rest not at all. A crawler inspects the root zone and the middle of the blade, and stops short of the tip, which is too narrow for any wheeled machine. What an internal blade inspection covers explains why the middle matters.
Time the turbine is stopped
A technician inspection of three blades is a working day, sometimes more, with the rotor stopped throughout. The time goes on the confined-space procedure as much as on the looking: entry, exit, rotation, re-entry.
With Detectra, capture takes about 15 minutes per blade, so three blades are about 45 minutes of capture plus the time to rotate and lock each blade. Up to 12 blades, four turbines, fit in one day on one set of batteries. The looking is moved out of the turbine entirely: review takes about 3 hours per turbine, at a desk, after the visit.
| Technician from the root | Crawler | |
|---|---|---|
| Coverage | Root zone only | Up to 80 % of blade length |
| People on the turbine | Two or more, plus rescue cover | One operator, plus the site's normal crew |
| Person inside the blade | Yes | No |
| Rotor stopped per turbine | Most of a day | About an hour |
| Turbines per day | One | Up to four |
| Record | Photographs, no position | 8K 360° video, distance on every take |
| Review | On site, by whoever entered | At a desk, by whoever knows the blade type |
What drives the cost
Neither method has a single price, and this article does not quote one, but the cost drivers are clear:
- Turbine downtime. Every stopped hour is lost production, and the technician method stops the rotor for most of a day per turbine. Offshore, the difference is larger: see Offshore wind blade inspections.
- People and days. Confined-space work needs more people per turbine and more hours per blade. The crawler needs one operator, and more turbines are covered per day and per site visit.
- Access. Travel, and offshore the vessel, are paid per visit. A method that covers four turbines per visit instead of one changes the cost per turbine more than any hourly rate does.
- Review. The crawler shifts hours from the turbine to the desk. Those hours are cheaper, they are done by the right person rather than the available one, and with AI-proposed candidates in Fenestra that an inspector confirms or rejects, they are shrinking.
- Repeat value. A technician's photographs are one inspection. A distance-tagged recording is a baseline that the next inspection compares against, so the second inspection is worth more than the first.
The honest summary: the crawler costs less per turbine on downtime and people, and it produces a record that has value beyond the visit. Where a fleet has only ever had the root zone photographed, it also produces findings the owner did not know existed, which is the point.
When the technician is still right
A crawler documents; it does not repair, and it does not touch. There are jobs that still need a person in the root:
- Repairs, and the close-up verification of a repair by hand.
- Tactile checks: tap testing a suspect panel, checking a receptor connection by hand, tightening a fixing.
- The root zone in detail, where a technician can get close to every insert and a crawler is passing through.
- Anything found by the crawler that needs a hand on it, which is the normal sequence: the crawler finds and positions it, the technician goes to that position and deals with it.
The two are not competitors so much as a sequence. The crawler covers the blade and tells the technician where to go; the technician goes there.
Frequently asked questions
How much does an internal blade inspection cost?
It depends on turbine downtime, people and access more than on any hourly rate. A technician entry stops the rotor for most of a day per turbine and needs a confined-space crew; a crawler inspection stops it for about an hour and needs one operator, with up to four turbines covered per day. Prices are quoted per fleet.
How long is the turbine stopped for an internal inspection?
With a technician, most of a working day for three blades. With Detectra, about 15 minutes of capture per blade plus the time to rotate and lock each blade, so about an hour per turbine.
Does a crawler replace the technician?
No. It replaces the technician's entry for inspection, and it covers far more of the blade. Repairs, tactile checks and the close-up work at the root are still a technician's job, and the crawler's record tells the technician where to go.