Originally Posted by
RAT 5
This was posted by Skyjob in 2015.
The LEDs are important in both scenarios.
However the takeoff with flaps greater then 5 selected allows departures with full extended LEDs.
Retraction failures are possible, mechanical problems or an environmental "impact" could result in a situation where one or more LEDs may not retract to partial, subsequently preventing a complete retraction, something which can be verified on the overhead indicators in LE stay in transit.
On departure, there is thus a risk that there could be one or more fully extended LEDs which you wil not find out about until retracting flaps up as I am sure you will not look during flap retraction on departure at the overhead panel to confirm partial retraction has been achieved...
Thus to prevent an inadvertent acceleration beyond 230kts with the potential that a fully extended LED is present, Boeing decided to prevent VNAV from accelerating above 230kts until LE TRANSIT/EXTENDED lights are extinguished.
On approach, the logic is in reverse.
The LE are retracted and extend to partial with the initial fall selections. They will only be fully extended with selection of flap 10, thus below 210kts, again preventing full extended LED in flight at speeds above 230kts.
Hope this helps
Thanks for posting it RAT5, just to add that this is valid for non SFP aircrafts only.