Reverse idle
Hello 320p,
Good question, good remark about habit patterns.
The elevated idle is activated by the thrust lever going to the reverse position, not by actual deployment of the reverser.
To give you an idea of the amount of thrust, see below:
(numbers for IAE V-2500, checked personally after TAM event)
Normal idle N1 – 22% N2 – 57%
Reverse range idle N1 – 27% N2 – 66%
About habit patterns: 21 years ago, the Lauda Air B-767 crashed due to inflight deployment of a reverser. After that, all B-767 worldwide flew with both reversers deactivated for a long time, about a year and a half. Boeing then specifically instructed to keep pulling the reverse levers to the reverse interlock stop, just to stay in the habit.
I do think the TAM accident has to do with habit as well: the PF had to do something out of the usual, pull both trhust levers to idle, then pull only one lever further back into reverse. In the half second that the movement would take, his hand made an execution error, left the one thrust lever "behind" just one step too soon. ("behind" in movement, so forward in position, if you catch my drift).
The post by Blinkz is wrong, or at least, not worded accurately: the thrust is elevated slightly, but certainly not to the value of "full reverse" when the reverse is not actually deployed.