Using VNAV on an Approach (Garmin G1000) Part II

by Brandon Ray · April 2, 2013

A Review of the Garmin VNAV Functionality, Part II

by Brandon Ray, CFAI+, CSIP, Master CFI, ATP, Gold Seal CFI, CFII, MEI, AGI

In my last article, we discussed some advanced functionality of VNAV for descent planning. VNAV is typically used for enroute descents and to meet crossing restrictions on descent. In this article we show an example of how you can incorporate VNAV on your instrument approaches as well. Before reading this article, I would suggest that you take a look at these two articles first:

Let’s look at a scenario approach and how you could fully automate the descents: RNAV (GPS 17) @ KWLD Let’s assume you’re at 4,000 ft in a G1000 equipped airplane with the GFC700 autopilot.
RNAV Approach KWLD

  • You load the approach via the ZALJO IAF (PROC: Load Approach)
  • You get cleared directly to ZALJO, so you activate the approach. (PROC: Activate Approach)
  • Autopilot is currently flying in GPS & ALT modes.
  • It automatically has ECUWO in the flight plan with an altitude of 3600 ft, and ICUJE at 3100 ft. It happens to show 4,000 ft. in white over ZALJO, because that is the altitude we will happen to cross the fix. (Not a target… Just a reference altitude)
  • You always have to make a choice regarding VNAV: Either Use it, Cancel it, or Modify it. Today is our lucky day, and they give you a clearance that allows us to fully use VNAV as it stands. “N12345, Maintain 4,000′ until established, you’re cleared for the RNAV GPS 17 approach.”
  • (When you hear the words “Cleared for approach”, this is typically the cue to arm the approach using the APR key on the autopilot)
  • Arming the approach adds the GP to the autopilot status bar so it is ready when we intercept the glidepath.
  • In the mean time you could either manually descend to 3,600 upon reaching ZALJO, or just let the VNAV do the descents for you. In this case, let VNAV do the work. The TOD probably lies somewhere between ECUWO and ZALJO. When you are 1 minute out from the TOD, you hear “Vertical Track”. This is our reminder to select the altitude and arm VNAV. Normally we would select the next altitude, but for this specific scenario, you can actually set 3100 (Refer back to item #7 above).
  • The autopilot now shows something like “GPS /// AP /// ALT GP/V”. Everything is now automated for the rest of the approach. The only step left is to manage power & configuration, enjoy the ride, and disconnect the autopilot and land… But I’ll go ahead and walk you through the progression of what happens with the Garmin.
  • The autopilot captures the Vertical path at the TOD (annunciated as VPTH on the status bar). While on the VPTH the armed (white) modes would be a condensed version of ALTV & GP. The ALTV indicates that the autopilot will level off at the VNAV BOD altitude of 3600 ft (@ ECUWO) rather than the selected altitude of 3100 ft.
  • The autopilot levels at 3600 ft. (probably won’t last long because the next TOD is coming up quickly)
  • There is no need to re-arm VNV for the next descent to ICUJE. Your altitude bug is already set. VNV is still armed from the last time you pressed it, and it will capture when it reaches the second TOD.
  • Autopilot captures the vertical path once again, and continues down to cross ICUJE at 3100 ft.
  • Passing ICUJE, VNAV goes away, and the glidepath is now available. As the aircraft intercepts the glidepath, GP captures on the autopilot and the airplane continues down the approach.
  • By the way, the autopilot ignores the altitude bug once it intercepts the glidepath or glideslope, so putting your altitude bug on the minimums doesn’t accomplish anything…(The autopilot will fly you into the ground unless YOU intervene.) Instead use your minimums bug for your visual reference on your minimums and use your altitude bug to select the highest altitude on the missed approach.

NOTE: Please note that this approach is not the typical GPS approach since it has the additional ICUJE fix, whereas most GPS approaches wouldn’t have anything in between ECUWO and MADFU. It is simply used to highlight a few special points on VNAV usage as it relates to WAAS approaches.

Keep in mind this type of VNAV use should only be attempted once you are fully comfortable with what to expect, and have fully briefed the approach. This method of flying an approach is simply an option – not a requirement. If you don’t have time, just cancel the VNAV and fly the approach like you always have. Don’t get so wrapped up in the avionics that you sacrifice safety or lose focus. Fly the airplane first! Everything else is secondary.

Another great resource is the Garmin G1000 PC Trainer. This allows you to try out everything on your computer rather than in the plane. If you have any questions in regards to this topic, just leave a comment below or find us on Facebook!

How it Started

One of my best friends in high school, (Doug Gray) was a private pilot. He offered to take me up for a flight in a 1967 Cessna 150, N6228S. We took off from Calhoun, Georgia, and he took me on a scenic tour of the area, I was hooked. I later found out that my English teacher, (Jan Haluska) was also a flight instructor and the school was offering a ground school course the next year, which he taught, along with flight training with the goal of becoming a private pilot. I managed to talk my dad into funding the training, at the time the total cost was right around $500. Cessna 150 rental rates where $12 an hour, and the 172 we used for cross country was $15 an hour including fuel.

Training Begins

It started August of 1977. The fall semester rolls around, and I am enrolled in ground school, and if memory serves me, we met twice a week. First came the paperwork for my student pilot certificate, which at the time was included with the 3rd class medical. I loved ground school, especially learning navigation, plotting courses on the sectional, again this was before iPads and GPS, so we did a lot of dead reckoning and VOR navigation for cross countries. At the end of the course, I made an 83% on the Private Pilot written exam, remember this was before we had the question-and-answer books that on future test I would consume before taking a written.

2022.06.09 11.19 Flyhpa 62a27fea7716a

Flying

The fun really began on August 22, 1977, it was my first flight. To my surprise we used the same Cessna 150, N6228S that my friend Doug Gray had taken me for a ride in. The Cessna 150 had a standard VFR instrument panel, with one NAV/COM, and one VOR CDI. No intercom, so no headset, at the time I didn’t know what I was missing. I didn’t get my first headset until I started my instrument training in 2003. I was a big guy, I was 6’ 4” and weighed 245 lbs. but I do not remember being uncomfortable in the 150 even with the instructor in the right seat.

First flight lasted .8 hours, and we accomplished orentation, shallow turns, stability, and effects of flight controls. Over the next few months we added steep 720’s, slow flight, stalls, turns around a point, S-turns, emergencies, landings, (short field, soft field and normal).

Learning

At this point I want to talk about a training experience that still stands out. We were close to solo and were practicing takeoffs and landings. Turning base to final Jan got very upset at the way I was cross controlling the aircraft. Cross control is when you are in, say a left turn, and use opposite rudder to line the nose up with the runway. So, he had me depart the pattern and head east to the practice area, and climbing up to 5500 feet MSL, he had me slow down to just above stalling speed, start a left shallow turn and add right rudder. As the airplane stalled I had the strangest sensation, no roller coaster has ever come close, instead of blue sky in the windscreen I was looking at brown ground, and as far as I could tell we were upside down, through the terror of the moment Jan talked me out of the spin, controls neutral, oposite rudder, pull slowly out of the dive. As we leveled off he asked me what altitude we were at, as I remember it was around 2,800 feet MSL. Then he asked me what would happen if I experenced this on base to final in the traffic pattern. The answer was obvious, I would be a pile of wreckage off the end of the runway with a very short-lived aviation career. Needless to say this cured my cross-control tendencies.

Another training event the sticks out in my mind was the first time we did takeoffs and landings at the High School runway. The runway was 1,500 feet long, not sure of the width, but it seems like we had about 5 feet on each side of the wheels when on the center line of the runway. Landing from the south you also had to go between a cutout in the trees to be able to stop in time on the runway. After getting confortable landing here every runway since seemed huge. I remember landing at Chattanooga (KCHA) on a night cross country and commenting to Jan, that I felt like I could of landed sideways on the runway, it felt that large.

Very soon after this I started wearing old shirts to all my flight lessons, the reason for this occurred on February 8, 1978. The lesson that day was stalls, takeoffs and Landing. As we were taxing back in Jan told me it was time for my first solo. I was very excited, and after some last minute advice from Jan, including watch for floating on landing the plane will be light with him not in the right seat, complete 3 takeoffs and landings to a full stop. It was a blast, and at the end of my shirt was shorter in the back because Jan cut the tail out of it signed and dated my solo [an aviation tradition]. Total flight time accumulated on the day of my solo was 18.1 hours. I was now officially a pilot with solo priveleges.

In my next article I start cross country training, when Jan decided that it would be best accomplished this in the 172. Checking out in N5970R was like moving into a 747, this started a love affair with one of my faviriote planes to date. Since this time I have flown over 900 hours in many different models of the 172 and feel like I am stepping into an old friend every time.

More about Randy here: https://www.flyhpa.com/team/randy-delong/

 

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