Surveyors and drone (UAS) operators on construction sites: the wind call, at your height

As a drone pilot or surveyor, you make a critical decision every flight booking: whether to fly or stand down a survey flight. This go/no-go decision is typically made the day before the planned operation. The primary factor influencing this call is the wind speed at the operational height of your aircraft, often between 50 and 120 metres, assessed against your aircraft's specific wind limit.

A wrong call carries tangible costs. A decision to fly when conditions are unsuitable can lead to a wasted site visit and mobilisation expenses. In some instances, it can result in the loss of an aircraft, which is a significant financial setback. Conversely, an overly cautious decision to stand down when conditions are flyable means lost operational time and potential delays to client projects.

Your operational manual and the conditions of your authorisation, such as those from the Irish Aviation Authority for specific-category drone work, set the parameters for operation. The Wind Agent instrument provides the wind data you need to inform this decision, helping you to balance operational efficiency with the longevity of your equipment. It presents the wind at 120 metres for the next three days, with your aircraft's limit marked on the display.

For drone operations, the wind at your flight height, typically between 50 and 120 metres, is the critical measurement, not the wind at ground level. Wind speeds at these altitudes can be significantly different from what is observed at the launch point. Your aircraft's performance, image quality, and battery life are directly affected by the wind conditions at its working height.

Your aircraft manufacturer sets the operational limits for wind, which are detailed in your aircraft's manual. These limits typically specify a maximum gust speed at your flight height. For example, a common limit for a drone, as cited by Dronespec, is 12 metres per second for gusts at flight height. It is essential to input your specific aircraft's limit, derived from your own documentation, into the instrument.

The Wind Agent instrument provides wind data at 10, 80, 120, and 180 metres. For your working height, which might be 100 metres, the instrument interpolates the wind speed and gust data. This ensures you are viewing the most relevant wind information for your specific operational altitude, allowing you to compare it directly against your aircraft's stated limits.

The instrument provides P(above your limit) by the hour, which is the fraction of ensemble members that exceed your specified wind limit for that hour. This feature helps you assess the likelihood of encountering conditions that are unsuitable for flight. For example, if 20 per cent of ensemble members show wind above your limit, it suggests a low probability of exceeding it, allowing you to proceed with a planned flight.

If P(above your limit) rises to 50 per cent, it indicates an equal chance of conditions being above or below your operational threshold. In such a scenario, you might consider delaying the flight by an hour or two, or preparing for a potential stand-down. An 80 per cent P(above your limit) means a high probability of exceeding your limit, making a stand-down decision more likely and prudent to avoid a wasted site visit or potential aircraft damage.

The Agreement Spine on the instrument shows where different weather models agree or disagree on the forecast. This is distinct from P(above your limit). High agreement among models provides greater confidence in the forecast, while significant disagreement suggests higher uncertainty, which you might factor into your decision-making, especially when P(above your limit) is borderline.

Here is an example of how you might use the instrument to plan a drone survey:

• Tuesday 10:00: You check the instrument for a planned survey flight on Wednesday. Your aircraft limit is 12 metres per second gust at 120 metres. The forecast shows P(above your limit) at 20 per cent for Wednesday morning, increasing to 50 per cent by 14:00.
• Tuesday 16:00: You inform the client that the morning flight looks good, but there is a 50 per cent chance of needing to stand down in the afternoon. You advise them of a potential delay.
• Wednesday 07:00: You review the morning brief. The forecast for 09:00 to 12:00 shows P(above your limit) at 10 per cent, with mean wind at 8 metres per second and gusts at 11 metres per second at 120 metres. The Agreement Spine shows high model consensus.
• Wednesday 08:00: You confirm with the client that the morning flight is a go. You mobilise to the site.
• Wednesday 13:00: The instrument now shows P(above your limit) at 70 per cent for 15:00. Mean wind is 10 metres per second with gusts at 13 metres per second at 120 metres. You decide to conclude the survey early and pack up.
• Wednesday 15:00: While packing, you observe increasing wind. You are glad you made the call to stand down, avoiding a potential incident or loss of equipment.

Your operational limit for drone flights is a critical parameter that must be accurately entered into the instrument. This limit is not arbitrary; it is set by the manufacturer of your aircraft and detailed in your aircraft's operational manual. Additionally, your own operations manual and any authorisation conditions, such as those from the Irish Aviation Authority, will specify the maximum allowable wind speeds for your specific category of drone work.

For most drone operations, the relevant metric is the gust speed at your flight height. For example, many drone specifications, such as those cited by Dronespec, indicate a maximum gust limit of 12 metres per second at the operational altitude. You will type this specific value, derived from your official documentation, into the instrument. The instrument's preset height for drone operators is 120 metres, aligning with common operational altitudes for surveys.

By accurately inputting your limit, the instrument can then clearly mark this threshold on the wind forecast. This visual representation allows you to quickly see when forecast wind conditions, particularly gusts at your working height, approach or exceed your operational boundaries. This direct comparison is essential for making informed go/no-go decisions for your survey flights.

Maintaining a dated record of forecast and observed wind conditions, along with your decision to fly or stand down, is an essential practice for drone operators. This record serves multiple purposes, from demonstrating due diligence to informing future operational planning. The instrument provides a dedicated record page to capture this information.

After each flight or planned operation, you can record what was forecast, what was observed, the specific wind limit you used for your aircraft, and the call you made. This creates an auditable trail of your decision-making process. For example, if an incident occurs or if there are questions about a flight's conditions, this record provides objective evidence of your assessment and actions.

Furthermore, this historical data is invaluable for your own operational improvements. Over time, reviewing past forecasts against actual conditions and your decisions can help you refine your understanding of local wind patterns and the performance of your aircraft under various conditions. This continuous learning contributes to more efficient drone surveying operations.

Operating drones in Ireland requires careful consideration of the prevailing meteorological conditions, particularly wind. The country's Atlantic exposure means that strong winds are a common feature, especially during the storm season, which typically runs from October to March. During these months, the likelihood of encountering wind speeds that exceed drone operational limits increases significantly.

Specific-category drone work in Ireland is subject to authorisation conditions set by the Irish Aviation Authority. These conditions often include parameters related to wind limits, which you must adhere to. The national forecaster, Met Éireann, provides general meteorological information, but for precise, height-specific wind data relevant to your drone operations, a dedicated instrument is beneficial.

The seasonality of drone surveying in Ireland often sees peaks during the drier spring and summer months. However, even outside the main storm season, localised strong winds can occur. The Wind Agent instrument provides the necessary detailed wind forecasts to help you plan and organise your operations effectively.