Missed Approach, Second Approach: Re-sequencing the CDU

Boeing's supplementary procedure for changing an approach starts on this page: "The associated airport must be entered as route origin or destination. ARRIVAL page ... Select" (FCOM SP.11.13). One thing this trainer does not do is fly the go-around, so its route still reads KDEN to KPHX. On the aircraft, once the FMC's go-around logic is established, "the original destination airport (airport from which the go-around was just initiated) becomes the new origin airport allowing SID selection if a diversion to another airport is required" (FCOM 11.31.34). So in the aeroplane Phoenix sits on the ORIGIN row of the DEP/ARR INDEX after a go-around, and its arrivals are behind the ARR> on that row, the same prompt the FCOM describes for a turn-back to the field you just left (FCOM 11.40.22). Here they are behind the destination row. The same go-around logic also deleted "all descent altitude constraints below the current airplane altitude" and replaced them with predicted ones (FCOM 11.31.34), which is one more reason to look at the plan rather than trust the one you briefed.

Choosing an approach chooses its runway with it: the RUNWAYS row changes to <SEL>25L. Runway 25L is 7800 ft long against 11489 ft for runway 26. That is the real Phoenix tarmac (FAA charts AL-322 for both runways), and you will meet it again on APPROACH REF. Re-selecting, rather than just tuning the other localizer, matters because each approach brings its own missed approach. Runway 26: "Climb to 2500 then climbing right turn to 5000 on heading 030° and PXR VORTAC R-336 to AVENT/PXR 15.9 DME and hold." Runway 25L: "Climb to 3000 then climbing left turn to 5000 on heading 130° and PXR R-163 to POPKE/15 DME and hold" (FAA ILS or LOC RWY 26 Amdt 1, ILS or LOC RWY 25L Amdt 1H). Opposite turns to different holds: if the second approach ends in a go-around too, the box needs to be holding the right one. <SEL> marks a choice "selected for entry into the route, but not executed" (FCOM 11.43.15), and on your active route the EXEC light has come on with it. Until you execute, the box still holds runway 26. One honest difference from the aircraft: "Selection of the desired approach or runway deletes all other approaches/runways" (FCOM 11.43.13), and this trainer goes on showing the list narrowed to the I26 picked first time round; its row is a toggle, and releasing it is how this trainer gives the list back.

The supplementary procedure's next lines are "RTE LEGS page ... Select. WAYPOINT SEQUENCE ... CHECK. Modify as necessary to agree with clearance" (FCOM SP.11.13), and this is the line that catches surprises. The title reads MOD RTE 1 LEGS: "All <SEL> entries propagate to the MOD RTE and MOD RTE LEGS pages for subsequent execution" (FCOM 11.43.15). The approach you just chose is on the page in flight order: HAMEK, the intermediate fix, then the final down to RW25L, and after the runway the missed approach, with each database constraint in large font. NEXT PAGE shows the rest. Row 2 is a ROUTE DISCONTINUITY: this trainer's plan holds no en-route waypoints after KDEN, so nothing connects them to the approach. A discontinuity "exists when the FMC is unable to determine the route leg following a waypoint" (FCOM 11.42.7), and it is not cosmetic: LNAV "automatically disconnects" on "reaching a route discontinuity" (FCOM 4.10.13). On a second approach, with the crew busy and the aeroplane low, that is the last place you want the roll mode to drop out.

HAMEK is the IF of the ILS or LOC RWY 25L, at 12.9 DME on the I-RJG localizer (FAA chart AL-322, Amdt 1H). "Discontinuities are removed by linking the route segment following the discontinuity to the route segment preceding the discontinuity. The next desired waypoint from the subsequent route is copied into the CDU scratchpad and entered into the discontinuity" (FCOM 11.42.7). HAMEK is already on LEGS, because selecting the approach entered its legs into the flight plan, so you line-select it off its own row into the scratchpad rather than type it, and because it is already on the route the gap closes rather than moving down. The FCOM's own cross-check is worth carrying: "Entering a waypoint which does not already exist on the route moves the discontinuity one waypoint farther down the route" (FCOM 11.42.7). If the gap merely moves, you linked to something that was not on the approach.

"Correct the ROUTE DISCONTINUITY by entering or deleting waypoints in a sequence that provides a continuous flight-plan path. EXEC key ... Push. Observe MOD RTE or MOD RTE LEGS page changes to ACT" (FCOM SP.11.7). The ACT title is the confirmation: nothing staged, and a route that LNAV can follow to the new approach. The order is the FCOM's own: after an approach selection on an active route, "Selections should be executed on the RTE or RTE LEGS pages after linking any route discontinuities" (FCOM 11.43.15). So this EXEC commits the approach change you made on ARRIVALS together with the link, and I25L now reads <ACT> there.

"The displayed data is for the DEST airport and the arrival/ approach entered into the FMC flight plan" (FCOM 11.43.18), so it moved with your swap: the small KPHX25L label with 7800FT 2377M under it, and under ILS 25L/CRS the frequency 110.75, ident IRJG and course 258°. Those match the chart's LOC/DME I-RJG 110.75 and APP CRS 258°. Runway 26 was I-CWJ on 111.75 with the SAME 258° course, because the runways are parallel. So on this swap the course line proves nothing, and the frequency and ident are what tell you which localizer the box is holding. Check them against the chart now, while there is time to fix them.

GROSS WT "Normally displays the FMC calculated airplane gross weight. A manual entry of gross weight is allowed" (FCOM 11.43.18), and the line opened on the FMC's weight, 61.0. On the aircraft that figure comes down with the fuel used, so it would already read close to 59.5. This trainer burns no fuel, so its FMC weight is still the one PERF INIT held, and you enter the real one by hand. A manual entry lasts only while the page is shown: "Leaving and returning to this page replaces a manually entered weight with FMC computed gross weight" (FCOM 11.43.18). Watch the right-hand column: "Speeds are based on displayed gross weights" (FCOM 11.43.19), so all three VREF lines come down as the weight does. Now look at FLAP/SPD at 4R. It has not moved: it still holds the flap and speed selected for the first approach, at the first approach's weight. (The VREF figures here come from the trainer's model, anchored on the FCOM's worked example, rather than from Boeing's performance tables.)

"Vref, once selected, will not be updated. To obtain an updated speed, the current speed must be deleted or a different Vref selected or entered" (FCOM 11.43.19). That sentence is the trap in every second approach: the page shows a fresh VREF on the right while FLAP/SPD keeps the old one, and FLAP/SPD is the line that is used. Deleting it and selecting again is the FCOM's way of refreshing the same flap setting, and FLAP/SPD now reads 30 with the speed the flap 30 line shows for 59.5 tonnes. The CDU half of the second approach is done: the right approach and its missed approach in the plan, a route LNAV can follow, the right localizer on APPROACH REF and a VREF for the weight you are actually landing at.