Snowflake and Inverse C symbol on Instrument Approach Plates

Looking at the Reno, Nevada airport ILS approach for 16R, you can see that it has a snowflake symbol on the top left of the briefing strip and an associated temperature. This is common at airports where temperatures get very cold and can be a problem for pilots flying instrument approaches because as the air becomes colder, the pressure levels are closer together. This means that when you're flying the same indicated altitude on your altimeter, the true altitude will be lower, leaving you dangerously close to obstacles.



A look at the front of the approach plate book shows the meaning behind the symbol and how much altitude correction is needed to compensate for the colder temperatures. This compensation is required when the temperature reaches the temperature next to the snowflake symbol on that particular approach plate.

---

Another symbol to note is the inverse C on the bottom of the approach plate next to the circling minimums. This symbol means that this particular approach has been updated to (possibly) newer minimums that take into account higher true airspeeds with an increase in altitude.


The front of the approach plate book also explains that the circling radius is greater, especially for faster category aircraft on the approach and has a greater effect at higher altitudes when there would be a larger difference between indicated and true airspeed.