Area Navigation Systems (RNAV) — Page 276, Lesson 273

Let’s start with the waypoint definitions, because that’s the core of how the FMC builds your route. First, a place bearing/distance waypoint — we call it a PBD waypoint. This is a position you define by giving a bearing and a distance from a known reference, like a navigational aid or a reporting point. The format you type in is, for example, `TRN250.0/76`. That means: from the aid TRN, on a bearing of 250 degrees, at a distance of 76 nautical miles. The decimals are optional, but the bearing must always be a 3 or 5 digit group — so 250 or 250.0 — and the distance may be 1 to 5 digits. When you enter that, the FMC automatically designates the new waypoint as `TRN01`, assuming it’s the first or only position specified with reference to TRN. So the FMC names it after the reference aid plus a number. Now, a course interception waypoint. This is a position defined where the bearing from any valid database position intersects with a course — for example, an airway — or the bearing from another database-defined position. The input format is like `GOW167.0/TRN090.5`. Here, the FMC produces a PBD waypoint, which in this case would be designated `GOW01`. Again, the bearings must be either 3 or 5 digits. So you’re defining a point where two bearings cross — one from GOW and one from TRN — and that intersection becomes your waypoint. Let me show you the geometry. Now, let’s move to the climb phase. Normally in the climb, the VNAV, LNAV, and timing functions will be operative. VNAV is vertical navigation — it manages your altitude and vertical path. LNAV is lateral navigation — it manages your horizontal track. And the timing function handles things like ETA and required time of arrival. Here’s the climb page layout. On the climb page — labelled CLB — at line 1L is the planned initial cruising altitude, if one exists and the climb is active. At 1R is the current climb restriction. The suffix ‘A’ indicates altitude. So if you see `6000A`, that means 6000 feet altitude. At 2L is the economy speed for the climb. At 3L is any speed restriction, which defaults to 250 knots and 10,000 feet. That’s the standard speed limit below 10,000 feet. Any other speed or altitude restriction imposed by ATC can be input to 3L from the scratchpad — that’s the line where you type data before sending it to a field. At 2R is the ETA — estimated time of arrival — and the distance to go to the next position. At 3R gives the height error at the next point. For example, it might show the aircraft will be 310 feet low at that point. That’s a vertical deviation indication. The climb engine N1 is displayed at 4R. N1 is the fan speed of the engine — the low-pressure compressor speed, expressed as a percentage. So you might see something like `90.3/90.3%`. The prompts at lines 5 and 6, both left and right, direct the pilots to the other climb mode pages. And RTA stands for required time of arrival — that’s used if an RTA is specified by ATC, meaning you need to arrive at a certain point at a specific time. So, to tie it together: the climb page gives you your planned cruise altitude, your climb speed and restrictions, your ETA and distance to the next fix, your vertical error, and your engine N1 — all on one screen. The waypoint definitions we started with — PBD and course interception — are how you build the route that this page then flies along.