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AECG Forty Mile Wind GP Corp. Forty Mile Wind Power Project Amendments, AUC Decision 27561-D05-2023

Link to Decision Summarized

Wind Power – Safety


RES Forty Mile Wind GP Corp (“RES”) applied to amend, construct and operate the previously approved Forty Mile Wind Power Project (the “Project”) and the Forty Mile 516S Substation. RES also applied to split the Project into two phases (the “Amended Project”). The amendments included a change of the turbine model, resulting in fewer larger turbines.

RES further applied for permission to transfer the ownership of the Project, located near Bow Island, Alberta, to AECG Forty Mile Wind GP Corp. (“AECG”).


The AUC approved the applications from RES Forty Mile Wind GP Corp. and AECG, subject to conditions.

Pertinent Issues

The AUC had concerns regarding the safety risk to aerial application flight operations posed by wind turbines proposed to be located within five nautical miles of the Bow Island Airport (the “Affected Turbine(s)”). The AUC conducted additional process regarding the Affected Turbines and bifurcated the decision on the Amended Project. In Decision 27651-D01-2023, the AUC partially approved the Amended Project and the construction and operation of the 27 unaffected turbines for Forty Mile Wind Power Project Phase 1 (“Unaffected Turbines”). These turbines will be located more than five nautical miles away from the Bow Island Airport (the “Airport”). The AUC further approved the construction and operation of the Forty Mile 516S Substation and the Forty Mile Wind Power Project Phase 2, consisting of 21 turbines.

In this decision, the AUC considered issues associated with aviation safety at the Airport, which specifically refers to the safety of aircraft operations near the Airport. The AUC also considered issues of regulatory compliance.

In Decision 27561-D01-2023, the AUC concluded that the Amended Project was in the public interest, as its negative impacts could be mitigated to an acceptable degree or that the negative impacts were otherwise outweighed by its benefits. In Decision 27561-D01-2023, the AUC also held that any approval of the Unaffected Turbines, and any steps taken in reliance on those approvals, would not be considered in making the decision pertaining to the Affected Turbines.

This decision considered issues associated with aviation safety at the Bow Island Airport, issues of regulatory compliance and whether the approval of the Affected Turbines was in the public interest.

Did the Project Comply with the Requirements of the Federal Aviation Regulatory Regime?

In evaluating compliance with the aviation regulatory regime, the AUC considered two Transport Canada publications, namely the TP312 Aerodrome Standards and Recommended Practices (“TP312”), which is a standards document, and TP1247 Aviation Land Use in the Vicinity of Aerodromes (“TP1247”), which is a guidance document. The AUC determined that TP312 did not apply to the Airport.

TP1247 references a concept called an obstacle limitation surface, which is a protective area for take-off, approach and transition areas that surround the runways of certified aerodromes or registered aerodromes with published instrument approach procedures. It is defined as an outer area at an elevation of 45 meters extending at least 4000 meters horizontally from the Airport. The AUC determined that TP1247 does not bind the AUC and that it does not impose restrictions on the erection of structures or other obstacles near a registered aerodrome.

The AUC further considered the Canada Flight Supplement, a manual published by NAV CANADA, which is a federal not-for-profit corporation that owns and operates Canada’s civil air navigation system and provides air navigation services. This manual contains aviation information that is required for visual flight rules (“VFR”) flight but that is not included on visual aviation charts or maps. It contains graphical depictions of all certified and registered aerodromes along with information concerning navigation aids and facilities. This manual defines an obstacle clearance circle close to aerodromes. The AUC found that an obstacle clearance circle does not impose restrictions on the erection of structures or other obstacles near a registered aerodrome that does not have a published instrument flight rules procedure.

Based on the evidence in this proceeding, the AUC did not believe that compliance with existing regulatory standards is sufficient to determine whether the Amended Project poses risks to aviation safety and proceeded to assess the Amended Project’s impacts on aviation safety at the Bow Island Airport during takeoff and landing of aerial applicator aircraft.

Will the Affected Turbine Structures Impact the Safety of the Aviation Operations at the Bow Island Airport

The AUC considered if specific impacts to the use of the grass cross strips at the Airport should be considered as part of the assessment of aviation safety impacts. While the AUC determined the TP312 did not apply to the Airport, the AUC then determined if the Amended Project complies with the obstacle limitation surfaces as described in TP312. The AUC also examined whether any of the affected turbine structures constitute a physical obstacle that will create an unacceptable hazard within the circuits flown at the Airport.

The AUC acknowledged that, while the grass cross strips at the Airport are not published within the Canada Flight Supplement, they may provide additional options for pilots flying and landing during emergencies. However, since the grass cross strips are not published, they would not commonly be used by pilots unfamiliar with the Airport and its surroundings.

In response to intervener submissions, the AUC noted that ‘wake turbulence’ is not contemplated by the term “obstacle” used in TP312 and held that it would not consider wake turbulence as a relevant obstacle but may consider wake turbulence as a hazard to aircrafts for the assessment of aviation safety. The AUC then determined that none of the affected turbines would penetrate an obstacle identification surface.

An intervener, who was a commercial aerial application pilot operating from the Airport, submitted that clearing wind turbines near the Airport would not be possible for his aerial spraying company’s aircraft, when normally loaded for application, without some form of circling or diversion of the flight path. The AUC did not see sufficient support in the federal aviation regulatory regime for a turbine-free outer surface. The AUC accepted that the circuit flown by an aircraft depends on many circumstances, including weather and the type, weight and speed of the aircraft. The AUC acknowledged that pilots have to consider the Affected Turbine structures and other obstacles when completing circuits and that the aerial spraying pilots may have to change their current flight routes to fly around the Amended Project. However, the AUC also noted that these pilots typically fly only a portion of the circuit, mainly on takeoff and landing.

As a result, the AUC found that the Affected Turbines structures were unlikely to create an unacceptable hazard within the circuits flown at the Airport. The AUC determined that impacts to aviation safety at the Airport from the Affected Turbine structures will likely be minimal.

Will Wake Turbulence from the Affected Turbines Impact the Safety of Aviation Operations at the Bow Island Airport?

The wake characteristics of a wind turbine are created by the interaction between the blade and the air. In particular, the thrust produced by the spinning rotor disrupts the airflow, causing it to slow down (called the velocity deficit) and produce increases in turbulence intensity.

The parties disagreed on the distances and intensities at which an aircraft would experience wake turbulence from the Amended Project’s wind turbines. The AUC found that there is some difficulty in drawing inferences from the evidence to determine whether any of the wind turbines associated with the Amended Project are sited too close to the Airport. Based on the evidence provided, the AUC could not determine the distance at which the relevant turbines should be sited from the Airport.

Dr. Rogers, an expert for an intervener, provided a review of historical data and stated that the setback distances between the Amended Project’s turbines and the Airport would be consistent with setbacks used from turbines to airports at hundreds of existing wind farms in North America. The AUC determined that this evidence has limited relevance to the extent it supports the conclusions of the same intervener’s simulation study and literature review. The AUC placed little weight on this evidence considering the inherent limitations of anecdotal evidence of this nature.

Dr. Rogers further submitted an aircraft wake encounter simulation study (the “Simulation Study”) to simulate the wake encounters by an aerial applicator aircraft along different flight paths. The Simulation Study showed that turbine-added turbulence affects the aircraft by causing flight perturbations, which would be similar to those caused by routine atmospheric turbulence. Dr. Rogers argued that the simulated wake encounters did not yield flight disturbances large enough to pose a safety risk. Dr. Rogers filed a wake simulation he performed for all 22 turbines within five nautical miles of the Airport. The Simulation Study considered what was described as a notational worst-case scenario. While the AUC accepted the accuracy of the simulation, it did not accept that it was sufficient to establish that turbine wakes would not impact operations at the airport.

Based on all evidence in the proceeding, the AUC found that the amplified wake effect is not likely to result in a wake turbulence effect that is categorically different from what would typically emanate from a single turbine but that there will likely be an amplification effect with an unknown extent. While the AUC recognized the distance is somewhat arbitrary, it determined that a four-kilometer zone is a reasonable benchmark, within which to apply a heightened level of precaution concerning aviation safety risks, including wake turbulence.

The AUC acknowledged that under certain conditions, turbines T4 and T5 may produce a wake effect that could extend into the four-kilometer radius when aerial applicators are conducting operations at the airport. At specific wind directions, the wakes of Turbines T4 and T5 were likely to interact and cause amplified wake turbulence. The AUC found that this additive effect was likely to cause the most extensive penetration of wake turbulence into the four-kilometer radius. The exact nature and degree of penetration in different weather conditions were somewhat uncertain. As a result, the AUC found that it was necessary to consider the wake turbulence from turbines T4 and T5 from a risk analysis perspective. Regarding all other turbines, the AUC was satisfied that their distance from the four-kilometer radius is sufficient to ensure that any wake turbulence they produce will not create physical forces within the four-kilometer radius.

Will the Aviation Safety Impacts of the Affected Turbines Increase Risk at the Bow Island Airport to an Unacceptable Degree?

The AUC considered if the Amended Project compounds the practical and operational risks faced by pilots, such that the project results in unacceptable aviation safety impacts. The AUC evaluated the risk and hazard assessments submitted by interveners.

Risk Assessment Evidence

Interveners submitted varying risk analysis with differing definitions of safety and the severity of risks posed by the Amended Project. One intervener’s risk analysis concluded that aerial applicators would be more exposed to reduced airspace due to the frequency of airport usage and the number of arrivals and departures required to conduct missions. He evaluated factors including turbine wake turbulence, disorientation, distraction and frequency of airport use, from the perspective of an aerial application pilot operating from the Airport. He submitted that the project poses a high risk. The biggest problem was the number of risks appearing before a pilot at the same time. This intervener argued that, while expert assessments of risk and safety are useful, the assessments submitted in this proceeding did not consider the practical operational challenges faced by pilots.

The AUC acknowledged the differing views on the amount of risk from the Amended Project. The AUC noted that there was not one correct safety assessment and that the role of the AUC was to consider the assessments as guidance in respect of its own evaluation of safety impacts.

The AUC accepted the evidence that the operation of aircraft involves the simultaneous assessment of many different factors, and that in a particular set of circumstances the addition of one further factor may impair a pilot’s ability to safely operate. The AUC considered impacts to safety from this perspective, having regard to how the Amended Project compounds operational challenges.

The AUC accepted the evidence that concluded that any wake turbulence created as a result of the wind turbines would not cause imminent danger to aircraft operating out of the Airport but also concluded that wake turbulence impacts will generally only impact the safety of operations at the Airport, if the wake turbulence is perceptible within four kilometers of the Airport. The AUC concluded that wake turbulence from turbines T4 and T5 could impact a pilot’s ability to safely operate an aircraft when conducting operations at the Airport.

The AUC determined that approval of all Affected Turbines, other than turbines T4 and T5, was in the public interest. The AUC was satisfied that, with the exception of turbines T4 and T5 that can cast perceptible wake turbulence within four kilometers of the Airport, the increase to aviation safety risk posed by the Amended Project to the Airport was reasonable.

The AUC determined that turbines T4 and T5 have the potential to increase aviation safety risk to an unacceptable degree. To mitigate the risk, the AUC imposed to following conditions of approval for Phase 1 of the project:

AECG shall include a provision in the turbine shut-off protocol, in relation to arrivals and departures at the Bow Island Airport (the Aerodrome Provision). The Aerodrome Provision shall provide that requests may be made by an aerial spray applicator, to halt or curtail turbines T4 and T5, if all of the following conditions are satisfied:

  • The requested period to halt or curtail the turbines will occur on or between April 15 to October 1.
  • The requested period to halt or curtail the turbines will occur between 30 minutes before sunrise, and 30 minutes after sunset on the relevant day(s).
  • The wind speed is expected to be below 45 km/h during the requested period to halt or curtail the turbines.
  • The wind direction during the requested period to halt or curtail the turbines is expected to be at a heading between 100 degrees and 120 degrees.
Name Change Application

Following a share purchase agreement, AECG acquired all outstanding shares of the applicant, and the applicant was no longer a wholly owned subsidiary of Renewable Energy Systems Canada Inc. The applicant stated that it had undergone a corporate name change from RES to AECG. The applicant requested that the AUC transfer the Amended Project’s existing approvals to AECG and that any future approvals be granted to AECG.

The AUC approved the request to transfer the Amended Project’s approvals from RES to AECG.

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