Skyboy is correct.
Another poster wondered about VNAV exceeding the flap limitation for a flap 25 takeoff. VNAV commands flap placard -5 knots for take off (so for flap 25 and above acceleration altitude, VNAV commands 185 kts).
Another question was about engine failures and VNAV, the FMC does detect the engine out condition and VNAV commands Vref40+70 above the Engine Out Acceleration Altitude set in Take Off page 2. If there's an emergency turn then SPD INTV is used to prevent the acceleration. The other bonus of 10.8 and VNAV takeoffs is that the autopilot is available with a single engine on takeoff above minimum engagement height (400'). It works well and changes the habits of a lifetime on a 737.
As for the 230 kts limitation... It's not in the limitations since it applies to a non-normal condition. Hence, it's in the QRH, as mentioned, for a LE flap transit light illuminated with trailing edge flaps up, i.e. leading edge device fails to retract. VNAV's acceleration speed logic, makes logical sense: flap placard limit -5 and leading edge failing to retract protection. The leading edge flaps will always be fully extended and the leading edge slats will be partially or fully extended depending on the flavour of 737 for every takeoff. So the system is programmed to ensure that the leading edge devices are fully retracted before commanding an acceleration above 230kts. Watch the LED lights on the overhead panel and ask your colleague when the VNAV command bug moves from 230 to 250 kts.
Outwith VNAV, what you do with the MCP SPD window is what's limited by your fingers and your head. Before VNAV on takeoff and 10.8 logic, VNAV wasn't selected after takeoff until the TE flaps and LEDs were fully retracted for LE speed protection and UP speed was never more than 230 kts for even the heaviest variant, hence VNAV continues to demonstrates LED speed protection.
In respect of the approach, aiming or having to extend flaps at the limit speed points to a mis-managed approach. The limit speeds are limits, not targets, as previously stated. Extending flaps as the appropriate manoeuvering speed is approached is better practice and demonstrates better planning ahead - rather than the descent and approach anxiety commonly seen in some less experienced pilots.
As asked before, why would you set 240 kts before the flaps were retracted? What does it gain and aren't you contravening SOPs as well as the Boeing's directions in the FCTM? They designed it.
Mentioned previously: 240kts in FMC below FL100 is only pre-programmed for descent and it has 250/FL100 for climb on the 737. Look at instrument approach design criteria in ICAO 8168. The range of speeds for initial approach is 160-240kts for a CAT C aircraft. Cat D is 185-250. If a Boeing Cat D aircraft FMC also has 240/FL100 in the descent page then logically it's a buffer for the speed limit. Why is that "buffer" not applied in the climb? It's been a while and I can't recall for Cat D. Add to this that most Boeing Cat D aircraft using the MTOW logic for flaps up manoeuvering speed will have a speed of more than 250 kts when clean after takeoff. If that logic isn't used for Cat D then at most long-haul weights, the actual clean speed will still be >250.
Structural limit for -800 fully extended leading edge devices? The TE limit would apply and so the relevant limit would be the F30 limiting speed (175kts) for SFP and Flap 10 (210kts) for non SFP. For the purist, with no trailing edge flaps and fully extended leading edge devices, it would be another non-normal condition and the QRH for Trailing Edge Flaps Up Landing has a 230 kts maximum when the alternate flaps system is used to extend the leading edges.
Last edited by shlittlenellie; 19th Nov 2015 at 11:18.