BA A380 IFE Moving Map altitude
BA A380 IFE Moving Map altitude
Came bakc on an A380 from San Francisco this week. Once at cruise the altitude never settled at the exact figure eg 35000. OK, I accept the plane is in air and that 35000 actually means the plane is varying altitude slightly but what got my attention was that at 35000 it was reading around 35100-210 and at 41000 around 410200-3000. I'm guessing it's to do with the pressure setting but can anyone confirm?
Cannot talk for the 380 but on other BA types the displayed "altitude" figures on the IFE in the cruise are Flight Levels based on the standard altimeter setting (1013.2), so unless the 380 does things very differently the discrepancies you describe should be nothing to do with any altimeter pressure settings.
As you rightly say the real aircraft altitude might wonder up and down a few tens of feet from the target level but with the magnitude of errors described I wonder if it's just a bug in the IFE - the only other option for the "errors" you describe at and above 410 would be that the crew had got some form of "block clearance" to operate between levels - not something I've done on that route but it's a while since I've been that way so perhaps not completely impossible .
As you rightly say the real aircraft altitude might wonder up and down a few tens of feet from the target level but with the magnitude of errors described I wonder if it's just a bug in the IFE - the only other option for the "errors" you describe at and above 410 would be that the crew had got some form of "block clearance" to operate between levels - not something I've done on that route but it's a while since I've been that way so perhaps not completely impossible .
Last edited by wiggy; 21st Oct 2016 at 12:33.
The IFE on the A380 is not one I've encountered anywhere else on the BA fleet. The moving map has all sorts of options and need not cycle. I had it set to an overhead display of the map with an information panel overlaid bottom left containing the speed, altitude etc. The altitude always showed a precise number of feet, not a flight level or x number of thousands of feet (so 35112 not 35000 for example) and it fluctuated in a smallish band as one might expect from an autopilot trying to maintain a cruising altitude. As a complete layman it looked to me like it was not set to the standard pressure setting but was using an altimeter set to (e.g.) sea level.
To do that the IFE system would somehow need to know what sea level pressure was all along the route of flight....and on other BA fleets that's certainly not a value we'd routinely acquire (from ATC) and load into any aircraft system on a Longhaul flight, though it might be of interest over high terrain....So I'm left with options of the IFE perhaps using a GPS derived altitude, a block cruise clearance, or an IFE bug.
Sounds like One for a 380 and/or IFE expert.
That was my first thought too. The aircraft is maintaining a pressure altitude, and fluctuations in the IFE-displayed value could indeed suggest that the latter is being derived from GPS.
Must admit I would have thought GPS feed is possibly the least likely reason for what the OP saw but I thought I'd offer it up just in case it's a possibility with the 380 system.....
When the OP says he saw:
(presumably meaning 35100 - 35210) I could put that down to perhaps a slight overreading of the actual Flight Level but within (IFE) display tolerances, but:
is presumably 41200 - 43000 - then I'd put money on a slow cruise climb, and/or a block clearance or an IFE problem.
A question for the OP - did the displayed altitude start at the lower level and gradually increase to the higher value over time? If it did it's probably a genuine gentle climb. If OTOH it simply fluctated between high and low values I'd put money on the problem being the IFE simply not working properly...
When the OP says he saw:
35100-210
at 41000 around 410200-3000.
A question for the OP - did the displayed altitude start at the lower level and gradually increase to the higher value over time? If it did it's probably a genuine gentle climb. If OTOH it simply fluctated between high and low values I'd put money on the problem being the IFE simply not working properly...
Last edited by wiggy; 25th Oct 2016 at 13:03.
No, sorry Wiggy. We started at FL350, then I got some sleep and next I looked we were at FL390, another snooze and as we crossed from Canada to just below Greenland FL410.
It didn't matter what level we were at the altitude never showed the precise number of feet (e.g. 35000 ft for FL350). It was always above the FL value and it was fluctuating in a band of about 100 feet - probably a wider band the higher we went.
When we were climbing the value simply increased until we got to the assigned level. As we descended the value reduced in the same way.
I can accept the fluctuation but I was interested why, instead of fluctuating around 35000 feet we were fluctuating around 35150 feet. At FL350 I never saw it go below 35000 feet; I don't think it ever went below 35050 feet.
It didn't matter what level we were at the altitude never showed the precise number of feet (e.g. 35000 ft for FL350). It was always above the FL value and it was fluctuating in a band of about 100 feet - probably a wider band the higher we went.
When we were climbing the value simply increased until we got to the assigned level. As we descended the value reduced in the same way.
I can accept the fluctuation but I was interested why, instead of fluctuating around 35000 feet we were fluctuating around 35150 feet. At FL350 I never saw it go below 35000 feet; I don't think it ever went below 35050 feet.
That's probably what you were seeing IMHO.
Harrington
TBH you might be expecting too much from the IFE. The moving map is simply part of the entertainment system, AFAIK it isn't subect to all the checks and filtering that goes on with Flight Deck instrumentation these days and so it's quite possible a 150 foot error or greater in IFE displayed altitude may well be within system tolerances (if indeed there are any tolerances published).
FWIW I've seen similar missmatches on the IFE having just walked out of the flight deck and known for certain from all the flight deck altimeters that we were on or within 50 feet of the required cruising level.
If the error you saw was a small and consistent one then rather than thinking in terms of an esoteric reasons for the error such as GPS or pressure changes along the route I'd be much more inclinded to think the error may well be down to where the IFE gets it's static pressure/altitude data from (these days probably one of the data buses) and/or how the data is processed before display.
TBH I can't give offer up much more than the possible explanations I have already come up with because the IFE is very much a sub-sub system (albeit complex) and most "pilot's notes" contain very little about the IFE other than how to turn it and other cabin systems off in an emergency (e.g. smoke/fire drills).
It might be worth risking a polite ask in the tech forum and seeing if you get a reply from an IFE engineer.
TBH you might be expecting too much from the IFE. The moving map is simply part of the entertainment system, AFAIK it isn't subect to all the checks and filtering that goes on with Flight Deck instrumentation these days and so it's quite possible a 150 foot error or greater in IFE displayed altitude may well be within system tolerances (if indeed there are any tolerances published).
FWIW I've seen similar missmatches on the IFE having just walked out of the flight deck and known for certain from all the flight deck altimeters that we were on or within 50 feet of the required cruising level.
If the error you saw was a small and consistent one then rather than thinking in terms of an esoteric reasons for the error such as GPS or pressure changes along the route I'd be much more inclinded to think the error may well be down to where the IFE gets it's static pressure/altitude data from (these days probably one of the data buses) and/or how the data is processed before display.
TBH I can't give offer up much more than the possible explanations I have already come up with because the IFE is very much a sub-sub system (albeit complex) and most "pilot's notes" contain very little about the IFE other than how to turn it and other cabin systems off in an emergency (e.g. smoke/fire drills).
It might be worth risking a polite ask in the tech forum and seeing if you get a reply from an IFE engineer.
Last edited by wiggy; 26th Oct 2016 at 11:04.
