Foxy JAA ATPL FMS question

[Alex Whittingham]

There's a question in the JAA exams that runs like this:

Q. The database of a Flight Management System (FMS) is organised in such a way that the pilot can:

(A) read and write at any time in the database
(B) insert navigation data between two database updates
(C) modify the data in the database between two updates
(D) modify the database every 14 days

...and the given answer is (B). In struggling to explain why I have quickly reached the limits of my knowledge and started to struggle with assumptions. Any knights in shining armour that understand how the FMS works please could you have a look at
our forum (http://www.jals.co.uk/forum/showthread.php?t=901) and see if you can give me a better perspective?

[End_of_Descent]

Depending on software version, 737 FMS computers have the ability to store data entered by the crew. In addition to the permanent navigation database, a temporary and/or a supplemental navigation database are available. Data stored in the supplemental database is stored indefinitely, data stored in the temporary database is erased after flight completion. (The permanent navigation database will be updated by the engineers after 28 days.)

Data entered can be viewed by the SUPP NAV DATA and SUPP NAV SUMMARY pages of the FMC.

I think (B) might be refer to such functionality which is, I think, not common to all FMSs.

[Alex Whittingham]

Thanks. I thought that might be what they are referring to but the difficulty I have is, if it's the supplemental or temporary databases they are talking about, what is wrong with answers (A) or (C)?

[End_of_Descent]

I don't really know but I believe that (C) is wrong because the navigation database in the permanent navigation database is not modified. Instead, new data is added to the temporary or supplemental database.

I have no idea about (A). My best guess is that crew entered data can only be entered by certain pages but certainly not any time. And reading data is not possible as well any time e.g. when monitoring the IRS system via FMC pages. Just a guess ...

EoD

[His dudeness]

I think, the point is, that you can´t modify the database, but you can put in (and modify) navigational data.
UNIVERSAL calls the 2 different databases:
navigational data and pilot data
So everything YOU put into the machine is stored in the PILOT DATA and that is stored until you delete it, on the other hand one cannot modify the NAVIGATIONAL DATA, they will be overwritten on receipt of the next "cycle"

This principle is the same with the Universals, GNS-XLSes and the KNS660 I worked with.

[Wodrick]

I agree with HD the point is that the only way that you can access the Database is for read only. You can add or change waypoints as required but these are erased on shutdown. The only way to change the Database is to download a replacement, in every case I have ever come across every 28 days, so all answers are wrong apart from B

[BOAC]

I'm probably being over-simplistic, Alex, but as I see it, A C would allow the navigation data (which is 'quality assured') to be 'corrupted' by the user (pilot) and therefore NOT a good idea?
By restricting the 'guaranteed' database access to a revision cycle, as Wodrick says, the provider/manufacturer maintain database integrity 'in house'.

D is wrong as the database update requires engineering input with a data loader, and although technically a pilot COULD do it, I guess they are angling at this?

Thank heavens I don't need to do that exam stuff any more!:D

[mutt]

It comes down to liability, the manufacturer will not permit you to alter their database as they will have an extremely difficult time proving that the FMS data was correct at the time of departure and wasnt altered by a previous crew.

Any additions by crews are added as supplemental information and will be later erased.

I'm at a total loss as to why they ask these stupid questions :(


Mutt.

[Alex Whittingham]

...just be grateful you don't have to explain them! Thanks everybody, much appreciated.

[Waggon rut]

I see the questions still asked by the authority bear no relationship to what you actually do when flying. I have been flying the 73 for two years and have not got a clue what you have been talking about!

[oxford blue]

I think that the question refers to the following, which is extracted from a B737-400 tech document which the CAA FCL issues as a reference for the JAA ATPL Gen Nav and Radio Nav exams. However, if they really mean database, as opposed to just 'FMC', the only correct answer is 'none of the above'. Are you sure that the question was remembered correctly?



Stored Waypoints

Stored Waypoints are held in the navigation data base. They can be up to 5 characters. Examples are:

Waypoint Identifier - ie, the published waypoint name, such as GRICE, ANGUS, LOMON, etc.

Navaid Identifier - eg, CPT, OX, SAB

Runway number - 27 L

Airport ICAO identifier - EGLL


Created Waypoints

The crew can define ‘Created Waypoints’. These are entered into the Scratch Pad and the Line Selected into either the RTE or RTE LEG page. Examples are:

Place Bearing/Distance - eg - SAP 250/40, where “Place” is any identifier already stored.

Place Bearing/Place Bearing - SEA 180/ELN 180

Latitude and Longitude



Option (b) might be the answer if they are talking about created waypoints.

[BizJetJock]

As you say, a badly worded question. However, I think B must be the answer because it is the only one that refers to adding extra items rather than editing existing ones - definitely not allowed!!
The FMS's as designed by the avionics manufacturer will store all pilot entered waypoints, routes etc indefinitely. The aircraft manufacturers and in some cases even the airlines can specify the software option to delete all pilot data on shutdown to keep the memory from being clogged up with items that may never be used again.

[Alex Whittingham]

It turns out the wording is actually slightly different in the latest version, thanks Oxford Blue. The question is published in the specimen JAA Radio Navigation exam. The change is that the question no longer says 'The database of an FMS...' just 'The FMS...' Does that change the context? The examiners must have thought so.

The problem is that, as EOD and his dudeness point out, there are several Nav databases, there's a main read only database and various permanent or temporary read/write databases where the 'created waypoints' are stored. (B) is certainly the right answer, I just hoped I was missing something!

[RichT]

I have been flying FMS based aircraft for over 2 years. I have a degree in electronic engineering and computer science. I worked as a software consultant in the aviation industry before flight training. It took me 4 reads of this question to understand what the hell they were asking. B is correct but the 2 database updates bit is a red herring.

Your job just gets tougher Alex!!

[Global Pilot]

A few years ago I spent many a night burning midnight oil doing my national ATPLs. Being totally at odds with many questions, I just learned that A, B, C or D was the answer to questions I couldn't get my head around and believe me there were many such questions. Even the next day when we looked for clarification from our ground instructors we were just told to learn the answer because that is what the examiner is looking for.

It is really refreshing to see that JAA have retainded some of the history of the old national systems!!!

Well done for seeking out the correct answer but remember in the ol' exam just go with, in this case 'B'.