In this particular incident a couple of years ago they mention the thrust levers in CLIMB GATE.
What exactly does this mean and how many thrust positions are there ?
Whilst you’ll occasionally hear the comment that the Airbus thrust levers don’t move, that gives a totally wrong impression. They move in exactly the same way that Boeing ones do. I’m not sure that the angle of motion is, but the tips of the levers on the A380 probably moved about 25-30 cms or so. When the levers are fully aft, they are at idle (!). Push them forward most of the way, and you reach the first gate, which is CLB. Next up is only a small motion, which takes you to FLEX/MCT. All the way to the forward stop, and you reach TO/GA.
In a Boeing, for most of the time (but not all), and when the auto thrust is engaged, the thrust levers are driven by a servo so that they sit at the position that would give you that power setting if the auto thrust were not engaged. If the A/T want’s 50% power, then they are roughly 50% of the way through their range of motion. The upshot is that if you disconnect the A/T, the power won’t change because the levers are already that the position for the current power.
Airbus do it differently. I think the original reason was to save the cost and weight of the thrust lever servo. They work exactly the same as Boeing levers when in manual thrust. When the A/T is engaged, it’s allowed to use any power from idle to wherever the levers are. If half way, then that would be idle to 50%. That’s not the way they are meant to be used though...the A/T needs to be able to go from idle to whatever the correct maximum power for the stage of flight is....and most of the time, that’s climb power. FLEX is a derated take off mode, and sets a particular power that was set up in the FMCs during preflight. The autothrust is not engaged then in FLEX. It’s the next notch up from CLB. TO/GA is also not an A/T mode. If you push the levers all the way, you’ll get TO/GA, and the A/T if previously engaged is disabled. Auto thrust engagement occurs when the thrust levers are pulled back from TO/GA or FLEX to CLB.
MCT is at the same position as FLEX, and it is the thrust lever setting that you want after cleaning up from an engine failure. If all engines are running, and you push the lever from CLB to FLEX/MCT in flight, the A/T is disabled and the engines go to maximum continuous thrust. But, if an engine is shut down, the A/T remains engaged, but now its max selectable power is MCT instead of climb.
There are a number of ways that you can confuse yourself with this, especially as you don’t look at the levers as you move them. The thrust setting is shown on the primary flight display, so you need to get into the habit of actually reading it. If the engines are already at FLEX, and you want MCT, you need to momentarily pull them back to CLB, and then back up to FLEX/MCT. Any time that you go back to manual thrust, you have to ensure that the levers are moved to a position that corresponds with the current power, otherwise you’ll probably end up with an unwanted, and large, power increase when you press the disconnect switch.
On the other hand, there’s a big positive to this system. As there are no ‘go around’ switches for the pilots to push, you cannot change power modes without moving the levers yourself. So, the scenario that caught the Emirates 777 in Dubai cannot happen with the Airbus levers.
In the incident that you mention, the FO has failed to pull the levers back to idle as he’s flared. The A/T will remain engaged, and instead of letting you land, will increase the power. It’s why there’s the ‘Retard’ automatic call out if you haven’t done so by 10-20 feet.
Both systems have good and bad features. The AB system has the effect of removing the thrust lever position from the pilot’s mind, as it’s almost always being handled automatically. That can be noticeable for people like me with tens of thousands of hours. For young pilots who have spent their entire time on AB, it can convert the thrust levers into arm rests. In an ideal world, I’d like a mix of the two. The AB gates, coupled with the Boeing servo.
