Chris, an AviationChatter reader asked a great question about holding patterns:
I understand the hold entry, but what is killing me is trying to determine the “mental picture” of the actual racetrack when ATC says “Hold south on the 180 radial.” My heading is 155º in this example.
What does ATC saying “south” have to do with anything?
Well Chris, the compass direction “south” doesn’t have much to do with your holding pattern at all. It’s just extra language to clarify the hold and help you, the pilot, visualize the proper holding pattern.
So, what does “hold south” have to do with our holding pattern? Simple answer: the inbound and outbound legs (that is, the majority of the holding pattern) must be south of the holding fix.
Look at the image to the right. Notice that most of the holding pattern is located to the south of the fix? Our friendly air traffic controllers might have issued this clearance by stating “Hold south of the BNA 180º radial.” Then again, they may have simply asked you to “Hold on the 180º radial.”
So Why Explicitly State the Compass Direction?
Our friends in ATC will usually provide a compass direction to prevent confusion between radials and inbound legs. Heres’s a common mistake. The pilot reads back instructions to hold on the 180º radial, but fails to realize that the 180º radial extends from the station. Instead of flying a 360º inbound leg, the pilot spins the CDI to a course of 180º.
This changes everything. The airplane flying the wrong way and well out of the “safe side” of the holding pattern! Notice that the holding pattern is on the north side of the hold and requires a parallel entry. Had ATC asked the pilot to “hold south,” our unfortunate aviator might have realized his error.
Back to the question
Notice that I am assuming standard right turns as ATC did not specify a direction.
I generated a few more examples to clarify things below.
I created all these images with Hold Here, an iPhone app that computes holding pattern entries and bugout times.