INSTRUMENTS FLIGHT PLANNING
If you predicted arrival at MAI at 00+00, then your TWO-MINUTE PRIOR Call commences at
58+00. It is a good idea to keep a scan on your DME and check it at 58+00 to ensure that your
call is timely.
Now that you and the pilot have a two-minute warning, let us look at the MARK-ON-TOP report
the pilot requires at each checkpoint or NAVAID. Your MARK-ON-TOP report is required at
all NAVAIDs during an IFR flight. When navigating to a TACAN station, MARK-ON-TOP is
at minimum DME for direct navigation or when the TACAN needle passes either 90º benchmark
when leading turns. Point-to-point navigation uses the closest point of approach.
There are five bits of information the pilot requires at the MARK-ON-TOP point:
Turn right/left to a heading
Item (1) requires you to tell the pilot to turn left or right to a heading. That heading is the
heading to get the aircraft on the outbound course. In choosing a heading, you must take turn
radius, winds, and navigational procedures into account.
Item (2) is simply the actual clock time you pass on top.
Item (3) requires you to name the point you are passing.
Item (4) is the fuel quantity you predicted for the MARK-ON-TOP from your TWO-MINUTE
Item (5) is the NAVAID you use for your next leg. If turning onto an airway, the NAVAID
remains the same, if flying direct the NAVAID changes.
A typical MARK-ON-TOP Call sounds like this:
"Turn right 138o, time 00+00, Marianna, fuel quantity 600 lbs, NAVAID remains the same."
Note that we turned the aircraft to 138º to fly a course of 141º. A turn of 51° is involved
requiring a lead point to roll wings-level on course. The formula for a 90º turn is ½ of 1% of the
aircraft's GS plus minimum DME. However, since the turn is only 51º we must adjust the lead
point by some amount in an attempt to roll wings-level on course. One-half of 1% of 210 kts =
1.0 DME, but we adjust this to .5 DME (as 51° is roughly one-half of 90°). Now .5 DME + 2.5
TWO-MINUTE PRIOR, MARK-ON-TOP AND WINGS LEVEL CALLS