B737-800
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 502
Communication Breakdown
Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Procedure
Data collected from reports and simulator testing indicate that Pilot workload and altitude deviations can be reduced by using VNAV for takeoff. This bulletin supplements material presented in Distance Learning 4 for [year]. Starting the first quarter of [year]; VNAV will be the recommended pitch mode for takeoff. VNAV may be armed on the MCP prior to takeoff provided the following requirements have been met: 1. A valid flight plan has been entered. 2. Both flight director switches are set to ON. 3. Performance data has been entered and executed. 4. MCP SPD is set to V2. During the Before Takeoff flow; arm or verify VNAV. When armed; verify that VNAV is displayed in white on the FMA. Set the lower of the SID top altitude; maintain altitude; or ATC clearance altitude in the ALTITUDE window on the MCP. During the Preflight flow; ensure the heading is set to the expected departure runway heading.I confused this bulletin as a green light to use VNAV for departures. It states on the top to be communicated via [notification] when activated and I missed it. My First Officer and I; as well as other Crews I have conferenced with; have also confused this issue and have been using this new procedure as well since the bulletin was issued. Perhaps there could be more concise language as to when procedural changes will occur and when.The bulletin differences have always been confusing to me and it doesn't make it easier when they are so frequent in nature. More importantly on this issue is the procedure itself and here is why. I have used it with different modes and techniques for the last week and I have found a few flaws. First and foremost is that if VNAV is selected: armed for takeoff and used for the departure the aircraft will accelerate on speed during flap retraction and will climb at the programmed speed usually 250 knots or whatever restriction is on the departure. This is all fine; except when it comes to meeting the second segment climb requirements. Example is on a departure that has no speed restrictions the aircraft will accelerate to 250 knots as soon as the flaps are up instead of climbing at its flaps up maneuvering speed until reaching 3;000 ft.; to meet the second segment climb then accelerating to 250 kts. until 10;000 ft. It was never stated whether or not we are to be concerned with this profile anymore or not. That needs to be addressed.Secondly if we are; and I believe we are; then we need to have the weight and balance date auto populate the FMC to alleviate potential errors or have procedural guidelines as to how to manage the VNAV departure. The easy way is to open the speed window and manually select the climb speed; which works very well but there wasn't enough guidance on that issue and it actually requires more steps than the current procedure.This is a typical release of a not very well thought out and or managed new procedure that is intended to create less work and enhance Safety; but actually creates more work at a critical phase of flight; due to poor verbiage and lack of enough guidance on how the system needs to be programmed and managed; to do what it is intended to do. In the future; major changes in procedural operations; as this; need to be thought out and articulated more clearly and include full guidance on the steps needed to perform them safely.
B737 Captain reported that a procedures bulletin that had not yet been activated resulted in an inadvertent policy violation.