G5 Autothrottle question

[G3G4]

When the throttles come to idle at 50 feet rad alt, is that a function of rad alt only or the voice call out "50 ft"

Here's what happened, both times at an airport with 5000 ft or less runway.

On approach we got all normal call outs except for the 50 ft call out and both times the throttles did not retard. I'm trying to figure out if we have an auto throttle problem, rad alt problem etc. Any ideas? Or just a glitch in system. Again the both times this happened was flying into a short runway all other times they worked as designed.

 

[gutshotdraw]

I don't use the auto-retard feature for two reasons:

1) I still fly the G-IV from time to time and don't want to be in the habit of relying on it (remember the G-IV accident at TEB a few years back? Auto-throttles were ON at touchdown).

2) Every time I watch the other guy use it, the airplane floats and lands long. Every time.

As to your question, as I understand it, the radat triggers the auto-retard and the callout so I'm thinking there's a hiccup in the radar altimeter.

 

[fokkerjet]

Radio Altimeter in the G550:

[FONT=Swiss721SWA,Bold][FONT=Swiss721SWA,Bold]

5. Retard Mode​

[/FONT][/FONT]

The retard mode is used to establish a fixed rate of throttle retardation to the idle thrust
position during the aircraft flare on landing. The retard mode is used for AP/FD coupled
and non-coupled approaches, and it is activated based on radio altitude < 50 ft (i.e., gears
down, flaps > 31.5​

​

​

​

_).
When the aircraft touches down, and both throttle levers are located in the idle thrust stop,
the AT automatically disconnects in preparation for reverse thrust. If the aircraft touches
down without the AT retarding the throttles because of a failure to detect a landing
configuration or lack of radio altitude, the AT retards the throttles to the idle thrust position
when touchdown is detected (i.e.,WOWor both wheels spun up), before it automatically
disconnects. The AT remains engaged until touchdown, so it is available in the event of​

a go-around during the flare.

 

[semperfido]

Sounds like a problem in your system. I use them (and like them) all the time to touchdown, but on a 5,000 footer may be a little sporty due to float issue that was mentioned.

 

[G3G4]

I understand the float issue, I actually wasn't flying. I always like to go to idle at 100 ft on a short runway. But non the less they should have gone to idle at 50 ft rad alt. I was just curious why they didn't when the gpws missed the 50 ft call out. Rad alt was working. Maybe we do have a rad alt problem

 

[paulsalem]

Not a Gulstream driver. But our audible altitude call outs are based on the CA side radio altimeter.

 

[doublepsych]

rad alt issue can be no bueno...

I understand the float issue, I actually wasn't flying. I always like to go to idle at 100 ft on a short runway. But non the less they should have gone to idle at 50 ft rad alt. I was just curious why they didn't when the gpws missed the 50 ft call out. Rad alt was working. Maybe we do have a rad alt problem

There have been some occurences of false 0 indications on the RA causing retard of TLs on approach and ensuing accident, (or maybe just a goat rope). ref: 737 turkish airline accident...

 

[gutshotdraw]

There have been some occurences of false 0 indications on the RA causing retard of TLs on approach and ensuing accident, (or maybe just a goat rope). ref: 737 turkish airline accident...

Now I have a third reason why I don't use it. Hadn't thought of it before but I suppose it could anytime you're in full landing configuration.

 

[Jetdriver69]

There is a reason why you keep your hands on the throttles and thumb near the AT disconnect when you are using the AT on any approach. As a rule, I disconnect the AT at the 50 ft call just in case and on any gusty approach prior to 500 AGL. Concerning a float with the AT, someone needs to work on their technique. The GV will float massively if you are light and you overflare, so stay ahead of the aircraft, flare at a lower altitude when light and you will do just fine.

 

[fokkerjet]

The system is only as good as its operator. Like the autopilot, never trust the automation when close to the ground, which means that one had is always on the yoke, and the other hand on the throttle (in our SOP) anytime the RA is active. Also, know what mode you’re in, how the automation will comply, and what you’re actually trying to do. Seen people command a descent, while on autopilot, click off the autopilot and level off. All the computers know, is that you want to descend, hence the power is reduced (or at idle), aircraft is level and the pilot is wondering why the throttle aren’t reacting. I always get rid of the flight director when maneuvering visually, say on a visual approach, with no lateral or vertical commands left in the guidance panel, other than speed. Works great, and haven’t been surprised.

 

[G3G4]

I understand tecnique and it has never scared me before, I was just curious if anyone had experienced this before and what they found the problem was. I know its a computer and they all have hickups somethimes but they happened both times in the same scenario. just trying to figure out what the problem might or could have been attributed to

 

[Gulfstream 200]

Auto-Retard is a marginally neat feature that often shares its name with the people who tend to rely on it.



Never saw one that worked well in anything but perfectly still air and dont know many people who use it.

 

[gutshotdraw]

Auto-Retard is a marginally neat feature that often shares its name with the people who tend to rely on it.



Never saw one that worked well in anything but perfectly still air and dont know many people who use it.

I wish fewer of my cohorts in this fleet used it...

 

[LJ45]

I've never flown with Autothrottles, of course I never had a problem hearing the 50 foot call and easying the power back. hehehe

 

[fokkerjet]

It’s not rocket science, at 50', throttles begin to go to idle. Whether you’re crossing the threshold at Vref -10, or Vref + 20, the system pulls the power off at 50’. Now it’s up to the PF to determine if 50’ is where you want the power pulled off. I’ve worked with various autothrottle systems, ie: Dassault, Fokker and Gulfstream, and they all require the PF to be in the loop at the approach/flare/roll out.

FYI, I've been using autothrottles since the late 90's, and as I stated earlier, you need to know what you've set up, in order to get the desired results.

 

[ProFracPilot]

The system is only as good as its operator. Like the autopilot, never trust the automation when close to the ground, which means that one had is always on the yoke, and the other hand on the throttle (in our SOP) anytime the RA is active. Also, know what mode you’re in, how the automation will comply, and what you’re actually trying to do. Seen people command a descent, while on autopilot, click off the autopilot and level off. All the computers know, is that you want to descend, hence the power is reduced (or at idle), aircraft is level and the pilot is wondering why the throttle aren’t reacting. I always get rid of the flight director when maneuvering visually, say on a visual approach, with no lateral or vertical commands left in the guidance panel, other than speed. Works great, and haven’t been surprised.

Or, the pilots fail to realize until they stall the airplane that they had pickled off the AT. I believe it was an American crew caused an A300 to stall at 16000' back in the 90's due to this oversight (then their screens all went into reset mode leaving them with nothing but standby instruments to recover, but that was an additional issue after the upset occurred). If you think about it, this could happen much easier than most of us think.

Imagine you're in a SPD commanded descent with the AP engaged on an arrival, trying to make a crossing restriction. The AT's aren't quite back at idle, and you need a little more descent rate to make a crossing restriction. So you disengage the AT's to make sure they stay at idle. Then the crew gets some kind of distraction (you pick it; VIP comes forward wanting to ask about ground trans, yada yada - whatever). I know, it is hard to imagine both crew are going to miss the various and obvious cues of the aircraft slowing as it captures the altitude for the crossing (such as how unbelievably quiet it gets as you're slowing through 150 kts). Next thing you know, you have stick shaker activation. Unlikely to happen? Sure, it's unlikely. But if any of us were to accidentally stall a jet aircraft, I'm convinced this would be the likely scenario where it would occur. We implemented this stall scenario into our sim training: Clean, AP on, AT's off, hands off until sticker activation. Not necessarily difficult to recover from in a training environment, but remember if it is going to happen it is because both crew lost SA. Real life reaction time would probably be delayed.

In aircraft with fully integrated flight management, we become as much system managers as we are pilots. One procedure I use to help me manage the automation is if the AT's are off, my right hand doesn't leave the power levers. I'm sure most of you do something similar.

My experience comes from the GIV. I don't fly a GV, but I can see where it would take some time (if ever) for me to trust the auto-retard feature.

Just my .02.

 

[semperfido]

Auto-Retard is a marginally neat feature that often shares its name with the people who tend to rely on it.



Never saw one that worked well in anything but perfectly still air and dont know many people who use it.

I wouldn't say I rely on it, but I do use it in the G550. It's whatever you get used to. I can understand why some folks just can't seem to adapt. Now shall I bring up the HUD and the Flare Que?

 

[gutshotdraw]

I wouldn't say I rely on it, but I do use it in the G550. It's whatever you get used to. I can understand why some folks just can't seem to adapt. Now shall I bring up the HUD and the Flare Que?

Adapt? Why should I "adapt" to something that could cause a problem for me (especially when I jump back into a IV)? Engineers frequently do because they can, not because they should.

And what's a HUD? Oh yeah, that useless thing I keep smashing my head into when I'm in the left seat.

 

[fokkerjet]

Adapt? Why should I "adapt" to something that could cause a problem for me (especially when I jump back into a IV)? Engineers frequently do because they can, not because they should.

And what's a HUD? Oh yeah, that useless thing I keep smashing my head into when I'm in the left seat.

Do you have "steam guages" in your GIV/GV, or did you adapt to glass?

 

[fokkerjet]

Now shall I bring up the HUD and the Flare Que?

:uzi: