A recent discussion with a fellow pilot had me going down a rabbit hole to find an answer to a seemingly simple question.
In Canada every IFR flight must be filed with an alternate airport, regardless of the weather forecast at your destination airport. This is not the same as in the United States with their 1-2-3 rule where filing an alternate is optional.
When choosing an alternate airport in Canada special “alternate weather minima” apply which depend on the type of facilities and approaches available at the alternate.
The question came up because of a Foreflight Video (since corrected here) that made the incorrect assumption that you can use an LPV approach as a precision approach for the purposes of your IFR alternate. So why is an LPV approach not considered to be a precision approach in Canada?
The main difference between a precision and non-precision approach deals with how the pilot receives vertical guidance to the runway (from The Vertical Challenge). There are two methods:
- Geometric Guidance. The system maintains a constant angle relative to the runway regardless of altimeter errors due to non-ISA temperatures, mountain wave effect or altimeter setting errors.
- Barometric Guidance. Using your altimeter (which is error prone) to determine your approach angle relative to the runway.
|Geometric Guidance Approaches||Barometric Guidance Approaches|
|Instrument Landing System (ILS)||VOR/NDB|
|Precision Approach Radar (PAR)||Localizer (LOC)|
|Localizer Performance with Vertical Guidance (LPV)||RNP|
An LPV approach uses a Satellite Based Augmentation System (SBAS) (WAAS in North America or EGNOS in Europe) to determine your altitude. It’s accurate enough for this approach type to have minimums as low as 200′ which match the performance of an ILS approach. So why isn’t this approach type considered to be a precision approach (just like an ILS?)
Lets wind back to 2013 when LPV approaches were starting to gain traction in Canada. Transport Canada issued AIC 700-003 which guides pilots and operators on how to adhere to ICAO standards for RNAV/PNB type approaches. Section 4.3 gives us a hint:
Note. At the time of writing this document, ICAO was considering the possibility of including this type of approach in the category of Precision Approach, instead of APV.AC 700-003 Section 4.3
And there we have it. Canada is waiting on ICAO to reclassify the LPV approach from an “approach with vertical guidance” to a Precision Approach. Until then, our flight planning will have to be based on LPV approaches being a non-precision approach.
(Note: Technically LPV is not a type of approach (you’re doing an RNAV approach) but I use the term here since it’s what is colloquially used.)