Airbus Ground Speed Mini Function
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- Опубліковано 7 вер 2024
- In this video we look at one of the fundamental functions of the Airbus auto thrust system, the Ground Speed Mini function. Allowing the aircraft to maintain a mini level of energy during approach in gusty conditions, by varying the engine thrust levels in respond to ground speed calculations. We explain the concept behind the GS mini function and take you through a scenario explaining, illustrating and calculating all the parameters. We show side-by-side the PFD speed scale, the engine parameters on the E/WD and the MCDU approach page values.
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Best explanation ever, Hands down.
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great video, very helpful. But I think there's an error at 16:30. I think you mean 140+ (20-20) = 140.
Hi James,
I went back to check and the calculation in the video is correct. It can be a little tricky though to understand. Let me try and make it clearer.
VAPP Target = 140 +(GUST) -> VAPP Target = 140 +(10-20)
The 10 represents the headwind (HW) in the example and the 20 is the reported wind inserted into the MCDU by the crew, the value that does not change. You see, ''gust'' is the difference between current wind and reported wind.
One should then argue that the value should become 130 right? 140+10-20 = 130. BUT this is not true as VAPP cannot be less than 140 in the scenario given. For the ground speed to not drop below 120kts. (GS minimum) the aircraft must maintain an IAS of 140 kts. If the aircraft slowed down to 130 IAS the GS would actually be 110 kts. Hence below GS Minimum.
A bit complicated and thankfully something the aircraft does automatically. We as pilots are just thankful to have the function :)
Man, this is such a great explanation. Well done. Very clear and well communicated. Other explanations I've heard discussed the calculations without setting up the information of HOW GS Mini allows the aircraft to maintain the proper momentum.
Thanks! Appreciate the feedback. Don't forget to check the Academy where you'll find the full theoretical A320 type rating course. academy.mindspacex.com
Just want to say big thanks for your work and knowledge share!
Appreciate the feedback. Don't forget to check the Academy where you'll find the full theoretical A320 type rating course. academy.mindspacex.com
GS mini has nothing got to do with A/THR , even if A/THR is inop we have GS mini, the only thing is speed should be managed.
It is hard to find a specific statement in the manuals, as it is not written directly, but it is an interpolation of the systems and their working principle:
GS Mini is a function that when used properly uses the A/THR system (automatic variations in thrust) to target a managed speed. For the speed to be MANAGED the A/THR should be active. Therefore, with A/THR inop you must use manual thrust and while GS Mini can be maintained with manual thrust this is not common pratice.
The first column on the FMA will read SPEED. During normal approach using the C/L we ensure A/THR is ON and in the correct mode so we have the benefits of GS Mini.
I hope this clarifies it.
@@MindSpaceXAviation no my friend. Managed speed is calculated by FMGC and shown on PFD. A pilot can disconnect ATHr and still fly managed speed using manual thrust. Suppose we are flying @6000 ft and managed speed is 250kts with auto thrust. 250kts is shown on PFD in magenta . I can disconnect autoTHr and still fly managed speed . If I reduce thrust by moving thr levers , the speed will reduce but the magenta target spd will be still 250. So basically, managed speed is a term used for speed by FMGC, if we select speed from FCU , then it’s selected speed. None of this is related to auto thrust. Now GSmini , I can fly manual thrust approach with GS mini protection, provided I properly fly the Vapp speed target on PFD. If I do that, GSmini is assured. If HW dies out on short finals, if I maintain the calculated Vapp, my GS will never go below GSmini.
Hi @drleo81,
You are correct. Your knowledge goes deep and you are spot on. Very impressive. However, we need to be carefull what is communicated in terms of practices.
While GSmini can be maintained with manual thrust this is not common practice. We want pilots, at least initially in their training and career, to couple the two together so to think that A/THR and GS Mini goes hand-in-hand. Airbus recommends for normal operation that A/THR is ON so to take effect of GSmini.
IAS TARGET SPEED= GS mini + current wind
You are correct, however the manuals state the formula as: IAS TARGET = VAPP + GUST. So to ensure we we deliver the correct information, as per the manufacture, we have to state it as is. The term "current wind" is not as clear as we and Airbus would like. So they divide it into CURRENT HEADWIND COMPONENT (measured by ADIRS along the aircrafts longitudinal axis) and GUST. GUST is the current headwind component minus the headwind value set in the FMGS (Tower Headwind Component). And when the FMGS established the IAS Target for managed speed, then it uses the gust value, as the current 'mean' value has already been accounted for.