mike738

Re: 1 -- A frequently asked question is why the lower DU is blanked most of the time. One major reason is it'll come to life in the event of engine failure or exceedance, and provides another visual cue that something has occurred. Engine failures in the cruise can be fairly subtle compared to losing one at V1, so it's a "pop-up" indication to supplement the other cues. We don't cover the DU even when blanked (unless it's very temporary) for this reason. Mike Archer

As has been stated already, it's an "or above" constraint. In the LEGS page, this will be immediately obvious by an A or B, for above or below, e.g. 8000A or 8000B. It's also possible to get a block constraint, such as "between 6000 and 7000", which will be represented in the LEGS page as 6000A 7000B. Something we do for profile awareness - if you have a constraint like the one you mentioned and you want to see where the FMC is actually expecting the aircraft to be, delete the constraint (without EXECuting) and the 8000A will change to a small font estimate of where it'll actually be on profile (around 15,000' it seems). Then erase the change so the constraint remains. Mike Archer

Yes, if the airline wants that option. Paper tables are still used, however many operators (mine included) use the Boeing Onboard Performance Tool (an iPad app) for all takeoff and landing performance data. Mike Archer

The key point to be understood here (which I believe now is) is that the guidance cue IS used in the exact same fashion as a conventional flight director (if you were responding to me saying "exactly"). You're very correct in saying that following the HGS cue is a different game to following the FD bars, but they're both command guidance to be followed to recapture or follow the desired flight path, which is where the confusion lay before. From the HGS manual: "The guidance cue symbol is the "Flight Director". It functions in the same way as a single cue Flight Director, but is designed for control of flight path. For the pilot, the objective is to capture the guidance cue inside the Flight Path circle using pitch and roll control inputs". Mike Archer

Exactly!

If they're not aligned, yes, you need to correct your flight path so they are aligned. If they are aligned, yes, you're flying where you should be, but you're not necessarily on the approach path yet, if you've somehow left it. The ONLY actual indication that you're on the localiser and glideslope are your LOC and GS deviation scales (or equivalent for non-ILS). Having the cue inside the FPV does not indicate that you're "on slope". If you keep them aligned though, you *will* end up on slope. Another example: you've somehow ended up really low. You immediately correct attitude so the guidance cue is inside the FPV. You're still very low, but if you keep them aligned, the aircraft will return to the desired approach path, same as if you were following the FD bars. Hope I'm not muddying things up for you. Mike Archer

You are correct in your statement that if the FD is centered, this may be commanding a correction to get back on path - the guidance cue is no different, except it's shown as a flight path correction rather than an attitude correction. Example: if you're one dot low on slope, the FD will command a nose up attitude change to regain the slope. Similarly, the guidance cue will command a shallower flight path (maybe 2 degrees instead of 3) to achieve the same. Once back on slope, the FD will command attitude to maintain on slope, and the guidance cue will do the same with flight path. You're also correct in that the LOC and GS deviation needs to be continuously monitored regardless. In really simple terms, the FD tells you where the aircraft should point, and the guidance cue tells you where it should fly, and this includes corrections to path. Mike Archer

The Guidance Cue is the equivalent of the Flight Director in the HGS. It will give lateral and vertical guidance based on your Pitch and Roll modes, the same as the FD on the PFD, with one key difference - on the HGS it's giving flight path vector information, whereas on the PFD it's giving attitude (pitch and roll) information. To clarify using an example - if you're on the ILS and your modes are VOR LOC and G/S, the FD will be commanding, say, 1.5 degrees nose up to maintain the glideslope. The HGS guidance cue, however, will be commanding a flight path of -3 degrees, to achieve the exact same result. So think of them both as flight directors, driven off the same data, but representing their commands in different ways (attitude vs. flight path). Hope that makes sense. Mike Archer

To cover (3), in the RW the FPV is largely based on personal preference. Many have it on all the time - I generally have it turned off for takeoff, as the vertical climb path is largely inconsequential - in the takeoff we're flying an attitude to give us our desired performance for configuration and thrust, whether the aircraft is climbing on a 10 degree or a 12 degree path is not really important, and if we need to meet a tight altitude constraint, the VSD is the best tool to let you know how you're performing. I'll turn it on in the case of any engine problems - it's further confirmation one-inop that we're maintaining a positive climb. Where the FPV is very useful is during raw data approaches, or visual maneuvers without FD guidance. Unlike light aircraft, in a jet it's very hard to accurately fly a profile based on the picture out the windshield. For instance, on a level downwind in the circuit/pattern, we might be at flap 5, 6 degrees nose up at 60% N1. In this case we use the FPV to assist us in flying level (by sitting it on the horizon). Once it's time to descend on a 3 degree path, regardless of attitude, thrust or configuration, sitting the FPV at -3 degrees will show us we're flying a 3 degree slope. In short, it's confirming that the attitude and thrust you're using for the phase of flight is giving you the desired flight path angle. Mike Archer

Hi, The yellow (caution) range starts at 8.35psi, as this is the differential pressure that will be scheduled when the aircraft is cruising above FL370, and under normal operations this wouldn't be exceeded. In reality, the needle can sit a tiny bit into the yellow arc. Dan, at FL410 with a landing altitude of 50' set, it should be scheduling an 8.35psi differential. The lines on the gauge are 0.2psi each, so you may be reading 8.4 as 8.2. You are correct, at 8.75psi and no controller response, you'll get an AUTO FAIL caution, and automatic switching to the opposite pressurisation controller will occur. At 9.1psi the relief valve will open. Hope this makes sense. Mike Archer

Hi boeingflir and others. Long time lurker and user of PMDG aircraft for many years now, and I fly the 738 for a living. Thought I might be able to provide some insight into the above and some of the systems. Firstly, the N1 button on the MCP is rarely used at most operators. Its only common use would be setting climb thrust during a non-VNAV takeoff. With current and recent FMC software VNAV takeoffs are the norm, and VNAV tells the A/T to set climb thrust at the specified thrust reduction altitude (all engines operating). This can be identified by the leftmost FMA changing from ARM to N1 (which is in effect VNAV pushing the N1 button for you). About setting MCT with one engine inoperative - this is done manually after disconnecting the autothrottle. There are various techniques or flows to make sure this is all done - one such memory technique is ALMA, on reaching flaps-up maneuver speed, we go A/T out, LVL CHG, set MCT, A/P in. Some items may be done already, and they're not mandatory (e.g. we can happily stay in VNAV SPD instead of going to LVL CHG) and this isn't SOP, it's just one technique. Also keep in mind it's rare for TO thrust to be at or above MCT - setting MCT on the good engine is generally a nice increase over our TO thrust. If you're doing a full thrust takeoff and it does happen to be above MCT, you've got a 10 minute limit, which is plenty of time to get sorted. Hope this helps. Mike Archer