Garmin GFC 500 Autopilot Flight Overview

[Fly Boomer]

5 minutes ago, midlifeflyer said:

Dunno. I see two posts by you in this thread and neither talks about why your think it might not be legal.

Post I was responding to said "didn't know you could use TOGO on takeoff".  My point was they call it the TakeOff/Go Around button for a reason.  Don't care if you use it or not.  Don't care if it's legal.  Don't care if it's a good idea.  But some people use the TakeOff/Go Around button on takeoff because that's what it's for.

I need to get off this computer, eat breakfast, and have some coffee.

[Marc_B]

For clarification, TOGA does NOT engage the AP, but rather just turns on Flight Director.  So when anyone is using the TOGA button for take off this is different than engaging AP.

According to AFMS, AP should not be engaged below 800’ agl except on approach to land.

so we’ve really just talking about how best to set up flight director on takeoff before you engage AP. 

[ArtVandelay]

Yes, people do. And many think it's an excellent technique. That's a matter of personal preference. 
But why do you think it might not be legal to have command bars displaying a 7 degree departure pitch attitude on an attitude indicator?
 

I think flying using IAS is safer than a fix 7° climb angle.

[midlifeflyer]

On 12/24/2024 at 12:11 PM, ArtVandelay said:

I think flying using IAS is safer than a fix 7° climb angle.

For extended  stabilized climbs, IAS mode has many benefits for safety and efficiency.

But we're talking here about the first 800-1000' of a takeoff using a pitch /roll mode that is designed with enough of a safety buffer to handle the first stages of a go-around or a missed approach when you see nothing when 200' above the runway, both of which (from what I've read) historically carry more risk than initial takeoff and climb. I'm not worried about flying wings-level pitch for that.

When we start talking about this, we're talking about technique. Mine, long before flight directors was to fly pitch for  those three high workload events rather than chase airspeed indicators. Translating that to a FD, for me that TOGA. I guess one could if they chose, set the FD for target IAS before takeoff and twist the IAS know during the earliest stage of a go-around or missed approach, but that wouldn't be my choice.. 

[PT20J]

The GFC 500 enters one of two modes when the GA button is pressed. On the ground it will activate takeoff mode and annunciate TO. In the air it will activate go around mode and annunciate GA. 

The GFC 500 AFMS does not describe takeoff mode in the normal procedures, but it is described in the vertical and horizontal modes tables in the section 7.

Better descriptions are written in the pilot’s guides for the PFDs. Here’s the description from the G5.

[Marc_B]

@PT20J thanks for the page. I know they describe the mode but was trying to find if Garmin ever described a flow or stepwise.

Makes sense when using FD show a wings level 7 deg climb. Honestly I don’t think I usually pay much attention to the FD right off the deck.  Of course I’m not usually taking off in LIFR and that’s probably where it’s most helpful…if it’s remembered/used as pointed out. 

[midlifeflyer]

2 hours ago, Marc_B said:

@PT20J thanks for the page. I know they describe the mode but was trying to find if Garmin ever described a flow or stepwise.

Makes sense when using FD show a wings level 7 deg climb. Honestly I don’t think I usually pay much attention to the FD right off the deck.  Of course I’m not usually taking off in LIFR and that’s probably where it’s most helpful…if it’s remembered/used as pointed out. 

The thing about flight directors is that, in the GA community it's relatively new and was earlier relegated to more expensive airplanes.  Most of us learned without it and it takes an effort to get used to it.

Based on what I've seen in transitions, I think it takes even more effort than getting use to relying on an altitude tape when hand-flying.  Took me a good year or two until I got comfortable with using it consistently (which also means turning it off when not using it). When I see someone maneuvering with the FD pointing up and left and they go down and right, it's a safe bet they are not even seeing the FD, let alone using it.  OTOH, watch a pilot who earned a certificate or rating with one, and is using it,  and it seems most natural thing in the world..

As you probably know, the checklist has some flows but pretty much for the Go-Around/missed.

That takes care of the two reasons I like using it for normal takeoff. Muscle memory to push the button and the development of the additional scan habit.

 

[William Munney]

The correct use of the AP and FD is actually a pretty large discussion.  I will throw my two cents in and pass on what i have been taught and teach whenever I am asked.  I use these techniques all the time as do thousands of airline and corporate pilots everywhere.  They also transfer nicely to GA airplanes with AP/FD systems installed as many Mooney’s are.

To begin, the airlines and the military have been using FD’s forever.  It is a separate system from the autopilot and one more thing that has to be learned and managed if you are to use it correctly.  However, with the introduction of relatively affordable and advanced avionics that incorporate things like FD’s and autopilots with VNAV into general aviation, discussion about when and how to use the autopilot (AP) and the FD in general aviation are good to have.  Using the AP or FD without thoroughly understanding them may be more dangerous than hand flying in low IFR conditions.  Over the years some techniques and procedures have been adopted.

For the moment, I have to back up a bit and introduce “levels” of automation first (As it applies to GA):

Level 4:  AP and FD ON—NAV + VNAV  (Your GPS Navigator is totally in charge of the flight path laterally and vertically)

Level 3:  AP and FD ON—NAV + VS or IAS (GPS Navigator commands lateral Navigation/ You input commands to modify the vertical path)

Level 2:  Hand flying with the FD ON  (Used for Takeoff, Hand flown go arounds, visual approaches backed up by ILS)

Level 1:  Hand Flying with No FD.  (Raw Data)

Companies like Boeing, for example, which have done a fair amount of research with automation, always advocate for the highest level of automation while fully understanding that there are times when lower levels may be needed depending on the pilots needs and those of ATC.  Except for those conditions listed in Level 2 automation, they also recommend turning OFF the FD whenever the AP is off.  If you choose to use the FD, you should learn to manage it and follow the directions of the command bars.  Using the FD and flying contrary to its commands, or “looking through” it is highly discouraged.  Why?  Eventually you will learn to trust and like using the command bars and they will lead you astray one day if the pilot and the FD’s are in different modes.  Once you learn to use and trust the FD on a low vis ILS or GPS approach, there is no going back.  BUT, lets say you are hand flying a GPS approach to minimums and you have selected  NAV or HDG and VS instead of approach for your FD guidance.  You may find yourself off the desired lateral and vertical path and even in a controlled flight into terrain scenario.  This very thing has caused terrible accidents in the airline/ corporate world.

As i said at the top of the post, the flight director is a great tool.  Especially for the single pilot in IFR.  But, only if it is understood and used correctly.

As far as takeoffs and go-arounds, there are MANY automation techniques that you CAN use but only one that makes any sense to me:  (Assuming you have a TO/GA (takeoff/go-around) switch installed in the airplane).  It is also the one that has become common practice.

For any normal takeoff, IFR or VFR, the objective, while you are close to the ground, is wings level and a pitch attitude  that takes you safely AWAY from the ground.  By using the TO/GA switch as you apply takeoff power…..this is the very guidance you will receive from the flight director.  That is, wings level and a safe pitch attitude for climb.  You CAN preselect a heading if you have received one from ATC but I would NEVER select HDG mode on the ground.  Why?  Your flight director will command the turn on the ground before you even become airborne putting you in a situation early in an IFR climb (clouds) where you want to climb BEFORE you turn and the FD is commanding the turn NOW.  You can follow the FD and start your turn at two feet above the runway OR IGNORE the FD as you climb.  Neither of those is a good option.

The better option from the automation standpoint is the following:

SELECT TO/GA as you set takeoff power.  (Roll and Pitch modes are TO/ TO………wings level, pitch to safely climb)

Climb 500-1000’ above field elevation………SELECT ROLL MODE, (HDG or NAV) Verify FMA’s and performance 

SELECT PITCH MODE (IAS or VS)……..Verify FMA’s and performance

SELECT AP ON……no lower than the minimum engagement height.  (You should be in sync with FD by this point)

 

ON Go-Around:

SELECT TO/GA as you set go-around power…..follow the FD to a safe altitude……OR leave the AP ON.

SELECT ROLL MODE  (probably NAV)

SELECT PITCH MODE  (probably IAS)

SELECT AP ON (if not already engaged)

 

On the Takeoff or Go Around ATC does NOT expect you to turn or navigate before you have reached a SAFE altitude.  What is safe?  500-1000’ AFE.  Pre-selecting FD/AP modes other than TO/GA on the ground is not recommended…..by anyone.

Hope this helps..long post.

 

 

 

Edited December 26, 2024 by William Munney

[Marc_B]

Makes sense for use of FD with airlines. Even when hand flying there is usually a flight path that you’re likely wanting to follow.

Big difference with GA is that there are more times where I’m on a flight, but not really a path. 

[midlifeflyer]

8 hours ago, Marc_B said:

Makes sense for use of FD with airlines. Even when hand flying there is usually a flight path that you’re likely wanting to follow.

Big difference with GA is that there are more times where I’m on a flight, but not really a path. 

If you are not on a path and don’t bug headings and altitudes, there’s no reason to use it other than takeoff or go-around and good reasons not to.

I don’t agree with the applicability of everything @William Munney said to GA, but most of it tracks my thoughts on best use.  As far as I can tell, he did point out the danger of displaying the FD if you are not going to follow it.  

[William Munney]

So, to clarify, this is accepted wisdom IF you are using an AP/ FD system.  You are certainly not required to use it.  And, there are many times I do not.