But in the 737 Classic, the autopilot-flown single engine instrument approach, is neither fish nor fowl. The remaining throttle is operated manually and so are the rudders; while the ailerons and elevators and stab trim are on autopilot. In the simulator for example, we see the situation where the pilot changes the thrust manually to correct a speed trend. In turn, he then has to adjust the rudder position to correct for yaw.
Unless the correct amount of corrective rudder is fed in to counter yaw, the control wheel then turns automatically to hold the ILS localiser. This causes inevitable flight spoiler operation and thus unwanted drag. The whole event can then turn into what is beautifully described as a horses's arse. And that is because of crossed controls.
The 737 is perfect for picking up deficiencies in knowledge/training/skill due to this.
Most of the problems I have observed in the sim seemed to be due to pilots treating the autopilot as a 'pilot', rather than a tool to assist. This comes about for a number of reasons including laziness, lack of knowledge of A/P limitations, being overloaded, lack of adequate training or simply, incompetence - they need the A/P to do it for them because they can't do it themselves.
Once they have engaged the autopilot, some pilots seem to be under the delusion that they don't have to fly the aircraft anymore because they have handed control over to another 'pilot'. They then spend their time focusing on checklists & trying to make decisions, while the ailerons are getting further & further towards the stops &/or the speed is rapidly decreasing.
What you usually end up with is the aircraft turning in the oposite direction to what is commanded by the heading bug & the pilot then saying "what's it doing?" & "the autopilot isn't working properly". He/she then disconnects it, which usually leads to immediate flight path control problems, particularly if the speed has become dangerously low.
Know what does what and know how to use it, then choose the best. Ignorance will bite you hard. I still see guys playing the piano on the AFDS trying to find the correct button to make happen what they want. AND they still look at the button and NOT the FMA.
Absolutely correct RAT 5! Most pilots don't seem to realise that pushing the button on the MCP is the third step in the process, not the first. You have to first decide what you want or need to achieve, then work out how you are going to use the various A/P modes to acomplish that, & only
then, do you move to the MCP to engage the required mode.
And I agree, you must
always, always, always check the FMA. Pushing the button is what you
want; what is on the FMA is what you have
got.
Again it's lack of knowledge of the system &/or lack of training in how to use it properly.
As for V/S, a lot of pilots seem to be either unaware of the appropriate time to use it, or scared of using it at all. Also, Flight Level Change seems to be the only mode some feel comfortable using during descent, even to the extent of using it instead of VNAV Speed when something has changed the descent profile. They don't seem to grasp that, put simply, VNAV Speed
is Flight Level Change with some of the protections of VNAV path.