Intriguing mysteries around the FMC use are abundant. It is therefore the topic of this second post of the “Tutorial for Flight Simmers, Young Pilots, and Aviation Enthusiasts“.
What follows is based on Boeing’s terminology and systems, more specifically on the 737NG. There are many differences with Airbus (and other aircraft manufacturers), which will be the topic for another day.
|First of all, here are some abbreviations to not mix up :|
General functioning : keyboard, LSKs, scratchpad
The CDU consists of a keyboard and a screen for which preliminary explanations will now be given.
The inferior part of the keyboard is quite clear: a numerical pad, an alphabetical pad and some specific keys such as SP for space, DEL for delete (used to erase a whole line in the route for example), and CLR for clear (erases the last character on the scratchpad, then the complete line if we keep pressing it).
There are 12 keys for direct access to the FMC pages between the screen and the two pads ( INIT REF RTE CLB etc. – their name is usually straightforward but they will be explained in more detail later on anyways). We can also find there the PREV PAGE and NEXT PAGE keys, which allow to navigate in the different sub-pages of a section.
In addition, the 12 LSKs are located on each side of the CDU screen. These keys are called « LSK » for Line Select Key. A standard convention is used to designate each of them: first the line number, then « L » or « R » for Left and Right, respectively. For instance, LSK 3R refers to the 3rd key starting from above on the right side, and LSK 1L refers to the uppermost key on the left. Click on the picture on the left to enlarge it (opens in a new window).
The scratchpad is the line at the bottom of the screen (circled in green in the picture on the upper left). It’s a zone where the data that we want to assign to a parameter is temporarily written. When we type a number with the keyboard, it appears on the scratchpad. Then, we can press the needed LSK key to assign that number to the parameter of interest. It is on this line as well that the system communicates simple messages such as “DRAG REQUIRED“, “ENTER IRS POSITION“, and “STEEP DESCENT AFTER XXX“.
We should also mention the EXEC key and its light indicator : when the light switches on, this key allows to confirm/validate the data entered in the sensitive pages.
For our example, we’ll use the EBBR-LSGG route used in the previous tutorial.
Flight data : all the data is arbitrarily chosen for our example: weight, loading, weather, route, runways used, procedures, etc. are chosen to be realistic but are not to be followed as advice. In other words, prepare the simulation with all the available tools (FuelPlanner, RouteFinder, TopCat, PFPX, ActiveSky,…) and use the following as inputs for your situation :
|CDU PREFLIGHT: POSITION – Here we are!|
Since the MCDU is multifunction, its initial menu proposes many functions : we choose <FMC via LSK 1L.
After a quick verification of the IDENT page (airplane model, engine rating, database, software), we go to the POS INIT page via LSK 6R where we can input the airport and the gate where we are, as well as the IRS position (SET IRS POS). This means you are supposed to have positioned the IRS selectors on the « NAV » for them to be aligning.
Once EBBR is set in REF AIRPORT and 140 in GATE , we can see the position given to the latter : N50°54.1 E004°28.8; a rapid cross-check with the position given by the GPS (page 2/3) confirms that the positioning data is coherent (i.e. is the same). We can thus copy paste this position safely (e.g. by pressing LSK 3R then LSK 4R).
Let us now move on to page RTE , either by pressing on ROUTE> via LSK 6R, or by pressing directly the RTE key.
EN ROUTE – Here we go!
In RTE, page 1 asks us to input the airports of departure in ORIGIN and arrival in DEST , the flight number in FLT NO. and the runway in RUNWAY . The CO ROUTE line can be used to set a Company Route which would be stored in the system. We won’t use it here though.
We now press on NEXT PAGE to go to page 2 and start encoding the route, segment by segment. Note that we won’t use SID nor STAR at this point, our route goes thus directly to ROUSY, then AKITO passing through the points listed on the complete route. We therefore encode the following data :
Next, we press DEP ARR to go to the DEP/ARR INDEX page where we can choose first our departure via LSK 1L <DEP EBBR .
The page EBBR DEPARTURES lists all departures available at EBBR : the runways in the right column, and the SIDs in the left column. We want to select the 25R runway that we set by pressing NEXT PAGE then LSK 1R. The left column shows now only the SIDs connected to 25R.
Pressing NEXT PAGE a few times leads us to our desired choice : ROUS7C .
We now press the DEP ARR key again in order to go back to the DEP/ARR INDEX page where we can now choose our arrival with LSK 2R LSGG ARR> .
The page LSGG ARRIVALS lists the arrivals on LSGG: the runways and procedures on the right column, and the STARs in the left column. We select ILS 23 with LSK 4R. The left column now shows only the STARs connected to that approach.
We press LSK 1L and our STAR on AKIT2R is now selected!
Usually, it is preferable to go through the different segments of the encoded route in the LEGS page in order to ensure no discontinuity is present. If pieces of the route are separated by empty boxes preceded by THEN and followed by ROUTE DISCONTINUITY , we can join them if that is our plan. We only need to press DEL then the LSK key for the empty boxes to disappear and the segments to be joined.
The last step is to press RTE to go back to the main page where the option ACTIVATE> is now presented to us. As soon as we press LSK 6R, the EXEC light will turn on, waiting our confirmation for the constructed route.
Check next post for Performances!