Originally Posted by
Check Airman
HOLD is a fairly stupid mode IMO. They way they’ve programmed it just leads to higher workload on my part.
FLCH is typically used on descent and frequently, the thrust levers go right to idle when FLCH is selected as the attempt to change altitude in 2 minutes will be exceeded. That means the aircraft is at the commanded speed in the window, (which opened when you selected FLCH) with idle thrust and frequently, a fairly significant rate of descent.
HOLD means you can adjust the thrust manually as the thrust levers have been released and are now free to be manually moved by you. One sees it when FLCH is selected. After pressing the FLCH button, you will immediately see THR and FLCH displayed on the FMA(and hear the PF say “thrust flight level change” and see the thrust levers move to idle. Within a second or two, you will see the FMA change from THR to HOLD and hear the PF say “hold”.
You are now in command of the thrust levers while in HOLD, so your hand should be on them as pilot flying.
One might find this HOLD mode useful during descent. For example, you may be approaching the tops of some buildups and want to avoid going through them. Depending on the positioning of those buildups, you may be able to simply add some thrust manually and reduce the rate of descent from say 2500 fpm to around 1000 fpm for a minute or two and once clear, reduce the thrust to idle again and continue your idle descent with the cabin crew unaware of the turbulence you just avoided while they are still preparing the cabin for landing.
This HOLD mode capability actually reduced your workload as you didn’t have to change modes for your vertical deviation. Such a deviation won’t be quite as easy while in VNAV PTH, where a slow down in descent rate had you switching to VS and once clear back to VNAV.