737-800 service ceiling?

[mingalababya]

This is a photo of my Garmin 96C (left) and a 738's IFE screen showing the flight's progress (right) from Darwin to Melbourne. My question is, are we really cruising at FL420 or is there some kind of error on both my GPS and the IFE data? I thought the service ceiling of the 738 was 41,000 ft, and plus with a south easterly track, shouldn't we be cruising at odd flight levels?

http://i90.photobucket.com/albums/k277/mingalababya/P1020909xxx.jpg

Enroute Darwin to Melbourne on T25 just before SAPED and 475 NM from Melbourne .. at 42,000 ft?

http://i90.photobucket.com/albums/k277/mingalababya/P1020929xxx.jpg

The moving map display of my Garmin 96C showing waypoints inbound into Melbourne on H119.

[Tempo]

a) I doubt that any professional crew in Australia would fly above the aircraft's max altitude (I have no idea what the 737 max altitude is but I assume it is FL420 or above)

b) Non-standard levels are allowed in Australian airspace

[Aussie]

Sure looks like FL420 on ya GPS and the IFE.... and im also pretty sure the Ceiling on a 738 is FL410....

Maybe a QF or VB lad will help us with this one :ok:

[psycho joe]

Max operating Alt on a 7378 is FL410. However, that's a pressurization limit and not a physical limit so I'd say that you were obviously flying unpressurised to get up into a good tailwind.

As for the IFE...Flight tracking is a costly optional extra so some low cost airlines just display the same info on every flight much like a tv test pattern. As most people don't pay attention they dont realise that their East coast flight is depicted as a return flight from Bali.

[bdcer]

Most of the GPS units that I've played with (no barometric feed) aren't very accurate with the altitude. I think it has something to do with the geometry of the satellites, ie. the satellites used are usually fairly vertical & therefore the angle is too acute for accurate altitude measurement?!..Bueller..

[VH-XXX]

My Garmin's GPS reading is as good as 100% accurate atleast up to 15,000ft that I know of. Pretty sure I've been to 43k in a VB738 as I was thinking it was mighty high at the time considering the QF ones only seemed to be 30-35, assumed at the time it was the new 800 modelmaking the difference.

[43Inches]

Could have been at FL410 on 1013hpa. The GPS data shows actual elevation above MSL without the errors induced by being on 1013 and density variations. Does the IFE take ADC altitude input or pure GPS signal(no baro aiding)?

[porch monkey]

I can assure you that you weren't at 420, or 430. As pointed out earlier, 410 is a limit set to retain the 8000 ft cabin pressure at max differential. It will climb higher, but an 800 is thrust limited up that high, and we don't have too many test pilots where I work. At least not that I've flown with anyway. As for why the error? F@cknows! 43 Inches may well have it right.

[Pin37]

After following the AF447 accident on another thread, I have to ask the question, should I feel nervous at a height aleast approaching the service ceiling? and in this case appearing to go beond it. Would there be implications of getting too close to "coffin corner"?:eek: I know each design is different and weights and so on, but 42k is way up there. I dont fly the big shiney jets and rarely get higher than 14k, so untill reading about AF447 I had not given "coffin corner" much thought. What do you think?

[porch monkey]

In a word, NO! It shouldn't concern you in the least.

[PlankBlender]

My vote is with 43inches! :ok:

[TWOTBAGS]

Most definitely FL410 with the subsacle to 1013 hpa.

My only question is how on earth you got away with operating GPS inside the aircraft?

In my previous mob, the ladies behind the door would have had your drawn & quartered if they had of caught you, followed by being meet at the gate by your friendly police man.....

[The Green Goblin]

Typical clowns up the back, do you not listen when you are told electrical devices such as radio receivers and GPS units are prohibited at all times during the flight?

I bet you went home and flew the sector yourself on FSX patting yourself on the back thinking you could do a better job.

As for your GPS, it's not TSO approved so any information you receive is irrelevant.

On a side note, pretty light load if it's anywhere near FL410, who is bleeding money?

[mingalababya]

Could have been at FL410 on 1013hpa. The GPS data shows actual elevation above MSL without the errors induced by being on 1013 and density variations.

Ok, thanks for that. That probably explains it. If the area QNH would have been around 1032, then that would be a difference of about 570 ft from FL410. Include the other errors as explained by bdcer and that would explain it.

I bet you went home and flew the sector yourself on FSX patting yourself on the back thinking you could do a better job.

Don't you just love some characters on pprune? Ask a simple question and get all sorts of accusations. LOL!

[PyroTek]

Typical clowns up the back, do you not listen when you are told electrical devices such as radio receivers and GPS units are prohibited at all times during the flight?

In OP's Defence:

Correct me if I'm wrong:

What is the risk of having a unit which recieves line of sight signals but does not transmit anything back?
From memory they say "radio transmitters". They never said anything about GPS units. Brings me to the point, they say you may use your mobile phone in flight if it is in Flight/Offline mode.
Flight Mode blocks any signal being transmitted, however, the GPS unit can still "hear" the signals sent by satellites to it.

:ok:Pyro,

I suggest you have a ride as a clown down the back sometime

[flying-spike]

" The use of mobile phones or radio transmitting devices is prohibited during flight"

"All mobile phones should now be switched off. Those having a flight mode should be switched to flight mode prior to being turned off"

Pyro, I can tell you where to get a red rubber nose and big floppy shoes if you want them.

[increasedescent]

I'm with crew rest. The GPS would be providing true altitude. Plus any anomalies in the GPS altitude, you should be able to come up with a 1000 ft error somewhere.

ID

[KrispyKreme]

well i am going to back pyro up on this one..... there is no problems in using rx devices on the aircraft (GPS, ipod, etc).. Transmitting devices thats another story!.... Green Goblin i think before you start calling pax clowns maybe you should think that those clowns are the ones keeping you in a job....also maybe they should ban laptop's as well becuase i am sure that when people use them in cruise the forget to turn off there wireless adaptor:ooh:..food for thought

Krispy

[ForkTailedDrKiller]

This thread has to take the prize for the biggest load of drivel on here for some time!

Its kinda hard to believe that people who pretend to be connected to the sharp end of aviation can be so WRONG!

My Garmin's GPS reading is as good as 100% accurate atleast up to 15,000ft that I know of.

Must be a better unit that mine (any of them)! It is not uncommon for the "altitude" display on the GPS (eg 496) to differ from the altimeter by maybe up to 500' - I have had them up to FL180!. If the Boeing was at FL410 then I am not at all surprised that the GPS might say 42.03. It is pure co-incidence that it looks so close to FL420.


Could have been at FL410 on 1013hpa. The GPS data shows actual elevation above MSL without the errors induced by being on 1013 and density variations. Does the IFE take ADC altitude input or pure GPS signal(no baro aiding)?

:ok: That all makes sense to me!


My only question is how on earth you got away with operating GPS inside the aircraft? In my previous mob, the ladies behind the door would have had your drawn & quartered if they had of caught you, followed by being meet at the gate by your friendly police man.....

You can't be serious, surely! If so, I hope you are never driving anything that I am a pax on.

Typical clowns up the back, do you not listen when you are told electrical devices such as radio receivers and GPS units are prohibited at all times during the flight?

The briefing actually says "radio transmitters" not "receivers". GPSs are passive units that receiver a signal and transmit NOTHING but the very low level electromagnetic radiation that you might expect from any electrical device. I suspect far less than the average laptop - particularly if its Wi-fi is left on!

As for your GPS, it's not TSO approved so any information you receive is irrelevant.

That may be technically true but in 500+ hrs of having a non-TSO'd G296/496 alongside a TSO'd G430, I have never seen them differ by anything other than a very small margin.

" The use of mobile phones or radio transmitting devices is prohibited during flight"

....and exactly which part of a GPS is a mobile phone or radio transmitting device?

Pyro, I can tell you where to get a red rubber nose and big floppy shoes if you want them.

Spike, you obviously have experience with buying clown gear huh?


I think it must now be pretty common for 'clowns down the back' to use GPSs, as the trolley dollies dont seem to react as they once did. The first time I had one (with the antenna suctioned cupped to the window) on a Qantas 737 the following conversation ensued:

TD: Excuse me Sir, what is that?
Dr: Its a GPS!
TD: Sir, I don't think its permitted to use that on board an aircraft.
Dr: As far as I know it is, but I will turn it off if you wish. Could you please ask the Captain if its OK to use a GPS.
TD: OK, give me a few minutes.
Returns
TD: Sir, the Capt says it is OK to use a GPS while the aircraft is in the cruise but we require it to be turned off prior to descent, as we do for all portable electronic devices.
Dr: OK, no worries.

Smart guy that Captain - maybe that how he got to the left seat!

Dr :8

PS: My understanding is that the difference between the 'altitude' display on the GPS and that on the altimeter, whether set to QNH or 1013, is the datum to which each is relating.

[mingalababya]

If the Boeing was at FL410 then I am not at all surprised that the GPS might say 42.03. It is pure co-incidence that it looks so close to FL420.

Dr :8

Ok, fair enough but I'm just interested in why. As others have said, the GPS would be measuring true altitude above MSL and not FL above the 1013.25 hPa pressure level which I think is a good explanation.

[porch monkey]

Hey Goblin, you do realise that the 737 can get to Fl380-400 even if every seat is occupied, don't you? The fuel load essentially dictates in the end. 700's will easily have 390/400 as the optimum level on sectors as long as 2 hrs, with every seat occupied. Levels have very little to do with "bleeding money" as you seem to believe.:rolleyes:

[Capt Fathom]

Hmmmm.....

The Qantas Website does specifically mention GPS's

Electronic Equipment

All electronic devices, including PDAs, laptop computers, handheld games and toys must be switched off during take-off and landing.

Portable electronic equipment such as laptop computers (including WiFi and Bluetooth enabled devices), PDAs (without mobile phones),
personal music (for example, iPods) and electronic game devices may be used when the aircraft seat belt sign is extinguished after take-off and until the top of descent.

Radio transmission using personal communication devices (including walkie-talkies, two-way pagers, or global positioning systems)
is prohibited at all stages of flight, as it may interfere with the aircraft's communication and navigation systems.

[PPRuNe Towers]

Ummm, this, oh gosh, life at 410 stuff folks.

Has it not percolated through that the 2 biggest NG operators in the world with fleets of over 500 aircraft between them have instituted SOP's and operational changes to try and stop problems, err, staying at those altitudes.

If a major operator insists on recalculating all permissible flight levels based on 1.5vs because of well documented problems staying at altitude it's our hope that you're having a good look at what's happening elsewhere. Even a timely reminder of what's available on the N1 page if you find yourself high, slow and the speed won't build back up could really help you one day.

Rob

[ForkTailedDrKiller]

Radio transmission using personal communication devices (including walkie-talkies, two-way pagers, or global positioning systems) is prohibited at all stages of flight, as it may interfere with the aircraft's communication and navigation systems.

So as long as the 'Radio Transmission' feature of your GPS (if fitted!) is turned off, its OK to use the 'Nav' feature of the unit!

For the record, A GPS RECEIVER TRANSMITS NOTHING!

If you think otherwise - please post a credible reference that supports that view.

Dr :8

[grrowler]

I guess the really important issue here is why you would want to have a GPS fired up at all, especially showing essentially the same info as the IFE.

[PyroTek]

I guess the really important issue here is why you would want to have a GPS fired up at all, especially showing essentially the same info as the IFE.

Possibly because half the aircraft that fly do not have IFE?
Maybe to see if your GPS unit will work with a "window of view" as big as an airliner window.
To not have to wait for every data screen to come up to see details of the flight?
Maybe just to make your "max speed" reading on your GPS unit "888km/h" (as is on mine), and get people wondering how the hell I could drive so fast?:p

:ok:Pyro,
Anyway, Thread drift.

[mingalababya]

I guess the really important issue here is why you would want to have a GPS fired up at all, especially showing essentially the same info as the IFE.

What PyroTek said. :) Surely there's nothing wrong with being enthusiastic and passionate about aviation, is there? ;)

[VH-XXX]

I'm not at the pointy end of the smart stick Doctor, however my 296 altitude is brilliant and always within 50-80 ft usually, taking into account QNH. Also I only use the little aerial off the back of the unit on an extension as the large one causes radio inteference.


Can't believe that people on here must think that GPS's are transmitters, what's going on with these generation-y pilots! :ugh:

[porch monkey]

Ease up a bit Rob, we've had our experience with the so called "close to the limit" stuff. Given that, we still use 1.3, and use it with some intelligence. The problem has not repeated itself, education has been useful. I don't know that "well documented" necessarily is the case either. Just because another airline doesn't want to use 1.3, or wants to institute some other SOP, doesn't mean everyone should. How far down are we going to dumb it? How much discretion do we take away from the captain to fly an aircraft intelligently and efficiently? 1.3 works fine, like everything else about the flight, the conditions you find yourself in need to be monitored. Full stop.

P.S. I don't think this is the kind of discussion the OP was looking for.......

[walaper]

I have actually had a couple of pax over the last year or so to present a letter from casa to indicate that they were able to use their gps receiver with only the normal restrictions ie off for T/O, LDG subject to Capts approval which they duly received.

[The Green Goblin]

Which begs the question why would someone want to use a GPS up the back. You're told you are departing at xx and arriving at xx, you're also told what altitude you are flying at most of the time. Sit up the back enjoy the service or lack of, have a snooze and let the fellas or shielas up the front do their job without second guessing them.

A fella up the back with a GPS is almost as bad as when you are flying single engine charter and a PPL arrives with a WAC and headset (usually a bose I might add which makes the old DC look archaic) in their arm in hot anticipation of the flight.

GG

[TWOTBAGS]

To answer FTDK.....

My only question is how on earth you got away with operating GPS inside the aircraft? blah blah blah

What Fathom said...... thems the rules brother either abide by them or expect the consequences.

Oh and I hope you are never driving anything that I am a pax on

You dont have to worry about that, at about $4M per seat (and there's 10 of them) you could not afford it anyway!

:E

[VH-XXX]

If this has become a p-issing contest TWOTBAGS, my Dad's d-ick is bigger than your dad's d-ick so there.

I bet you have a great time flying around in your $40m aircraft with the flexibility to go where-ever YOU want whenever YOU want :rolleyes:

[ForkTailedDrKiller]

Radio transmission using personal communication devices (including walkie-talkies, two-way pagers, or global positioning systems) is prohibited at all stages of flight

thems the rules brother either abide by them or expect the consequences

You cannot break that rule unless you create a radio transmission by using your portable GPS as a "personal communication device"!

I am still looking for that feature on my Garmin III Pilot and Garmin 496.

Dr :8

PS: I wonder how many people turn off Bluetooth and Wifi when using a laptop on an aeroplane?
I suspect ................ NONE!

[Peter Fanelli]

I think it must now be pretty common for 'clowns down the back' to use GPSs, as the trolley dollies dont seem to react as they once did. The first time I had one (with the antenna suctioned cupped to the window) on a Qantas 737 the following conversation ensued:

TD: Excuse me Sir, what is that?
Dr: Its a GPS!
TD: Sir, I don't think its permitted to use that on board an aircraft.
Dr: As far as I know it is, but I will turn it off if you wish. Could you please ask the Captain if its OK to use a GPS.
TD: OK, give me a few minutes.
Returns
TD: Sir, the Capt says it is OK to use a GPS while the aircraft is in the cruise but we require it to be turned off prior to descent, as we do for all portable electronic devices.TD: Oh...and he said ONLY ONE!
Dr: OK, no worries.



Oh and for what it's worth, GPS units can interfere with other radios. Have experienced it myself. Cessna 310 with a Garmin 100 into Yalata once a month. With the GPS on it was impossible to cancel SAR, usually Perth on 6580 if I recall correctly, but as soon as the GPS was turned off HF worked fine. Just because an electronic device does not send a transmission to the antenna does not mean it's not capable of causing interference with other radios.

[gav_20022002]

This is comical, the guy asked a fair dinkum question. Were they really at FL420 or is there another reason for the alt indicated on the IFE and GPS, yet that Q&A gets lost after about 5 replies and now its a pure bitching contest, Go and start a new thread somewhere else and bitch about who has the bigger d!ck and use of GPS down in the cabin.

i opened this thread thinking someone might have actualy come up with a sensible answer instead its a sh!t fight!! Thanks for wasting 5 mins of my life for reading it. but since its so important to pilots and maybe makes them feel insecure that some guy down the back can get the same flight info as them they r worried. who cares!!!!! for all anyone knows he may have asked the flight crew upon boarding and they said go for it. why crucifie him for having a interest in aviation and comparing his data to the IFE??

but as for an answer to this, i did a flight from ML-BN, IFE said FL402, once we landed it tured out i knew the FO so iasked him what alt we were at and he said we were between FL370 and FL390 and the IFE reading is AMSL not 1013.


see ya on the flip side

[Ultralights]

i still dont know what the service ceiling of a 738 is yet!!!

You cannot break that rule unless you create a radio transmission by using your portable GPS as a "personal communication device"!
Iphone??? has GPS, WIFI, Bluetooth, and GPRS, though it doesnt like travelling much more then 100kts., cant update the map fast enough with the poor phone signal at any altitude really..

[PyroTek]

Iphone??? has GPS, WIFI, Bluetooth, and GPRS, though it doesnt like travelling much more then 100kts., cant update the map fast enough with the poor phone signal at any altitude really..

The iPhone isn't a true GPS though, it merely triangulates from phone towers, that is something that requires transmitting/receiving.
My Nokia N95, however has a true gps chip just under the * key - meaning that I can put it in offline mode, and it will kill wifi, bluetooth, or any other sort of transmission, however leaving the GPS chip alone to receive data.
This could be why QF says "GPS" devices under prohibited, because people don't know the difference between true "listen from satellite" GPS and psuedo "triangulate between phone towers" GPS, the latter of which requiring the initial transmission from the phone.

:ok:Pyro

(Time for thread to be split??:confused:)

[Boomerang_Butt]

Interesting. The cabin crew manual, at least at QF, states:

....Global Positioning System (GPS) receivers, pocket calculators and electric shavers are unrestricted. These devices may be used at any time. (my bolding)

I assume within the context of PED rules for takeoff/landing.

To clear up any confusion, as has been stated, if you have an iPhone with GPS, the device is classified according to its highest level of capability- i.e. it is a phone first & foremost. Won't post a direct quote here as we're not meant to reproduce the manual (controlled docs & all that)

I don't know much about it, but I have done CPL met & I was thinking 1013 could explain the high altitude. I wouldn't do it but I understand some people like to know exactly where they are. IFE maps are great for a general idea, but if you want accuracy or waypoints, a GPS will do it. Kind of wish the IFE was GPS-based, it would stop me having to call every lake & mountain I've never seen before 'Mt Diligaf' or 'Lake Farkall' :E

[ferris]

I doubt you would get a clearance to FL420, anyway. Non-standard non-RVSM level. That's something they suck in trainee controllers with in the sim ;)

[ForkTailedDrKiller]

This is comical, the guy asked a fair dinkum question. Were they really at FL420 or is there another reason for the alt indicated on the IFE and GPS, yet that Q&A gets lost after about 5 replies and now its a pure bitching contest, Go and start a new thread somewhere else and bitch about who has the bigger d!ck and use of GPS down in the cabin

The thread originator's question was answered and/or affirmed in Post #'s 7, 8, 11, 12 and 20!

Seems like a pretty good service to me! :E

Dr :8

[gav_20022002]

ok so it was answered why does it have to degenerate into a pissing match?

[blueloo]

For what its worth, this is the latest (and I don't think it has changed recently) policy on GPS's on QANTAS flights. This is from the QF Flight Administration Manual (under Cabin Management):

The use of essential personal medical equipment, electronic watches, cameras,
Global Positioning System (GPS) receivers, pocket calculators and electric
shavers are unrestricted. These devices may be used at any time.

This is further expanded on in a table, classifying these devices as Group 1 PEDs (personal electronic devices) - which classify phase of flight/boarding etc when these devices and the other categories can be used.

It is very clear that Group 1 devices can be used at all stages in the table too.

[Qansett]

The use of essential personal medical equipment, electronic watches, cameras,
Global Positioning System (GPS) receivers, pocket calculators and electric
shavers are unrestricted. These devices may be used at any time.

GPS and camera are in the Group 1 devices, aren't they?
Does it mean that i can use them during take off and landing??

What does Group 2 devices say?

[psycho joe]

You dont have to worry about that, at about $4M per seat (and there's 10 of them) you could not afford it anyway!


So you took half the seats out of an over-priced Otter? :E

[VH DSJ]

GPS and camera are in the Group 1 devices, aren't they?
Does it mean that i can use them during take off and landing??

Just make sure youre not flying with TWOTBAGS. With his outfit, you go to jail for having a GPS receiver onboard! lmao!

[blueloo]

Group 1: Yes at all stages (Boarding, taxi,takeoff, descent, landing, on ground)

Group 2:
Devices permitted for use inflight once the Seat Belt sign is extinguished after takeoff, until top of descent:

PEDs including:
• Personal computers, PDAs, electronic games,
music devices such as AM/FM receivers, Compact
Disk, Mini Disk and MP3 players, and one-way
pagers.

Wireless Local Area Network (WLAN) devices with
in-built WiFi access including:
• Personal computers, PDAs, and computer
peripherals.

Wireless Personal Area Network (WPAN) with
in-built Bluetooth access devices including:
• Personal computers, PDAs, computer peripherals,
headsets, GPS receivers, and cameras



(My underlining in last paragraph - so if the GPS transmits via bluetooth or wireless network then there are some restrictions)

Group 3 and 4 have more restrictions


There is one caveat I have not mentioned: Operational restrictions may be applied by the Captain!

[ZappBrannigan]

My only question is how on earth you got away with operating GPS inside the aircraft?

In my previous mob, the ladies behind the door would have had your drawn & quartered if they had of caught you, followed by being meet at the gate by your friendly police man.....Sorry, had to respond to this bit. I've played around with my handheld GPS at least 3 or 4 times on QF long haul sectors - and once, the CSM actually sat down next to me and messed around with the unit himself - had a good chat about avionics and all things aircraft. Not a single issue with them.

Also had them out a couple of times on the friendly jumpseat up the pointy end at Virgin - not a single issue there either.

[FJ44]

Been interested to read some of the explanations in this thread.

Flying regularly at FL450 the GPS altitude display is normally around 47100 feet, this is on two G530's, both with 50' of each other and also an old Pilot III (just to see what it said)

Is the gap between each pressure level still 30' feet at altitude? Or is it larger as the pressure decreases? If you were at FL450 and had some one exactly below at FL430 would the RAD ALT read 2000 (as an example of measuring the distance between the aircraft using something other than the altimeters) or slightly more?

I've found that the GPS altitude is quite accurate below about FL150 but always over reads the higher you get.

[mingalababya]

Group 1: Yes at all stages (Boarding, taxi,takeoff, descent, landing, on ground)

blueloo, thanks for digging that up. I really couldn't understand what all the fuss was about with having a GPS receiver on board. If it was an issue, then I'm sure the flight attendants would have asked me to turn it off. To get a decent reception on these things, you have to have it hard pressed against the window most of the time, so there is no way that you could get a decent signal and conceal it from view of the FAs.

For me, tracking the flight with my humble Garmin 96C GPS is a good way to pass the time. I don't know about others, but I do find it interesting to know where I am, and what towns I'm passing over, even when I'm pax. Some people prefer to read a book, some prefer to sleep, some (geeks, propeller heads) prefer to GPS; we're all different. :)

[Old Fella]

Am I the only one who noted the post (#4) of Psycho Joe in which he suggests the aircraft was flying unpressurised to get up into a good tailwind? Mate, you have to be joking, surely. Just how many of you are professional aviators, or even aviators?

[ZappBrannigan]

Am I the only one who noted the post (#4) of Psycho Joe in which he suggests the aircraft was flying unpressurised to get up into a good tailwind? Mate, you have to be joking, surely. Just how many of you are professional aviators, or even aviators?Well, Virgin's cabin safety demo does use the phrase "for your comfort the cabin will be pressurised" - so obviously they traded a little comfort for an increased tailwind :)

[VH-XXX]

I've been flying unpressurised for years Old Fella, maybe that's why my brain got squashed and I didn't notice the stupid comments on here.

[Old Fella]

To Psycho Joe & ZappBrannigan, I trust you were each commenting "tongue in cheek", as VH-XXX obviously was.

[ZappBrannigan]

To Psycho Joe & ZappBrannigan, I trust you were each commenting "tongue in cheek", as VH-XXX obviously was.Can't speak for PsychoJoe, but I certainly was :)

You just reminded me of the DJ "for your comfort the cabin will be pressurised" line, which always made me chuckle a little.

[Boomerang_Butt]

As I posted earlier, I find it interesting that the QF website seems to contradict both the crew manual & the airports manual... I guess an email to the manual revisions and/or website department is in order!

I've had people using GPS on board, if in doubt then I just ask that they not use during t/o & landing... I'll have to check but I'm pretty sure on the back of the safety card it says GPS are ok...? Just no Furbys, apparently! :}

[ForkTailedDrKiller]

I've been flying unpressurised for years Old Fella

I, on the other hand, pressurise and de-pressurise the Old Fella as required, depending on the circumstances! :E

Dr :8

[Socket]

I think you are all on the wrong track. If it is a Quaintass 737 it's service tops out at crappy and is usually somewhere between nonexistant to rude. At least it has been in the last 15 years or so.:}

[ZappBrannigan]

I doubt you would get a clearance to FL420, anyway. Non-standard non-RVSM level. That's something they suck in trainee controllers with in the simOn this topic, what about FL410 when it's a non-standard level? Don't fly anything that can get up that high (yet, hopefully), so not really up with the "rules" here - but I've been up front on a VB B738 from OOL-MEL, planned level was FL400, we were granted FL410 due to bumps supposedly from a JQ A320 that departed immediately ahead of us on the same track to MEL.

Edit: on reflection this seems weird/incorrect since (correct me if I'm wrong) the 320 can't cruise at FL400 anyway - anyway, it's beside the point, it was bumpy at FL400 and they gave us FL410.

[psycho joe]

Am I the only one who noted the post (#4) of Psycho Joe in which he suggests the aircraft was flying unpressurised to get up into a good tailwind? Mate, you have to be joking, surely. Just how many of you are professional aviators, or even aviators?

Thanks for bringing that to my attention Old Fella, you're quite right.


I should have written de-pressurised. :O

[Hempy]

Discussion of Vertical GPS Accuracy

Consumer grade GPS receivers can provide very accurate horizontal positions, especially when augmented with WAAS and left to average the position over a period of time. However, the same is not true for vertical position. There are a number of causes for this, and this page attempts to explain them in simplified language.

Definitions

The ellipsoid is the simple, smooth model of the earth based by first defining the basic ellipse describing the Earth's shape to a best fit, then second, describing the volume derived when one rotates the ellipse about its semi-minor axis. If we didn't have topography, this ellipsoid (some cartographers and GIS packages call it "spheroid") would well-describe the shape of the earth. The geoid, on the other hand, is an undulating surface, roughly where the sea level would be (accounting for local gravity variations, caused by density variations in the earth's crust, but not water variations), if the land didn't get in the way, referenced to an absolute gravity model. It is an gravitic equipotential surface.
The sea level, is another undulating surface, which is different than the geoid due to temperature, current, wind and salinity differences in the water. However, the sea level doesn't work on the land!
When we formally speak of vertical, the vertical we speak of is the orthometric height. This is an algebraic result of subtracting the geoid separation (difference in geoid and ellipsoid height from the Earth's centroid of mass at a given surface point) from the ellipsoid height.

GPS Workings

GPS, because of the math, works from the smooth WGS84 ellipsoid directly. The height it offers, unless it tells you otherwise, will be an ellipsoid height (distance from the Earth's centroid of mass to the surface of the ellipsoid) as determined by the functions of trilateration and free-space ranging. However, I think that most user grade receivers have a built in geoid model and perform the adjustment. You may be able to tell by looking at the $GPGGA NMEA sentence -- see NMEA protocol information (http://www.gpsinformation.org/dale/nmea.htm) for more information. This NMEA sentence (sometimes) reports the difference between the geoid and the ellipsoid at the current location. If, on the other hand, one were to use the multi-frequency, geodetic quality GPS systems, one only uses the autonomous measurements to get into the ballpark for timing and position, then uses a network between multiple receivers located on well-surveyed sites where the cartesian coordinates are well-known (at least for the purposed of a given survey). Then, once again, one calculates the cartesian coordinates of all receivers in the survey, including the unknown point, creates a fairly rigid geometric network among the various points, and performs a least-squares adjustment to determine the parameters of x, y, and z for the point of interest. Beyond that, one generally transforms the coordinates from cartesian to one of the more conventional forms: geographic, state plane, transverse mercator, etc., for textual and graphical dissemination.
GPS determination of height using a commercial, consumer grade GPS is problematical for several reasons.
3d positions are calculated using the code-phase method, where one uses the pseudorange between satellite(s) and receiver at a given epoch to determine a position. If 4 satellites are in view, the procedure is straightforward. If more than 4 are in view, then most receivers "over-determine" the position using all combinations of 4 satellites from those in view to establish positions, and then perform yet-another-least-squares-solution to attempt to determine which satellite combination is best. This combination is tested periodically to make things better, but usually not tested each and every solution.
Using code-phase, however, allows for a larger error budget which contributes to the overall error of autonomous positioning. In general, to get good 3d positioning, one would want a satellite directly over head and 3 others below the horizon in a constellation similar to the structure of a statically-depicted carbon molecule. All 4 hydrogen bonds are at ~120 deg to each adjacent bond. Since GPS signals don't traverse dirt too well, that's impractical for surface-based receivers.
Since most satellites used in conventional consumer-grade hardware are selected for being somewhat above the horizon, accuracy of vertical determination suffers.
We've consistently seen horizontal accuracies of 6m or better ever since Selective Availability was switched off in 2000. However vertical accuracies of 10-20 meters are not uncommon because of A) the problem cited about constellation selection being inconsistent for vertical determinations... and B) the problem of using the increased error-budget laden code-phase solutions.
Using geodetic receivers, a good network for adjustment, long-period (4-8 hours) data acquisition, data decimation to remove autocorrelation effects, and careful postprocessing to achieve good solutions to submit to least squared adjustment, you can readily achieve 1cm horizontal and 3cm vertical accuracies. But you'll never do that with anything from the consumer product line, unfortunately

For a more scientific discussion on why aircraft still use pressure instruments and not GPS to determine altitude see http://users.erols.com/dlwilson/gpsvert.htm

[bdcer]

Yeh Hempy, that's wot eye ment! I'm just not that elokwent

[porch monkey]

Joe, just keep digging that hole. You'll get there eventually.....:rolleyes:

[psycho joe]

At the risk of being accused of gross narcissism in quoting oneself:

Max operating Alt on a 7378 is FL410. However, that's a pressurization limit and not a physical limit so I'd say that you were obviously flying unpressurised to get up into a good tailwind.

As for the IFE...Flight tracking is a costly optional extra so some low cost airlines just display the same info on every flight much like a tv test pattern. As most people don't pay attention they dont realise that their East coast flight is depicted as a return flight from Bali.

Clearly I am the P!ss taking.

You see the original post described a flight from Darwin to Melbourne, yet the picture of the IFE in the original post looked as though it may have been depicting a flight from Bali.

You see on one hand I was saying "Who gives a rats @rse what your gps says. And on the other hand making a gentle jybe at LCC's / "New age carriers", and the value of "Flight Tracking" to the loathsome masses in general. :ugh:

[Qansett]

Blueloo... thanks for answering my questions!

When I was on the a QF plane, a QF cabin crew told me to turn off the camera (it's a Group 1 device with no bluetooth and WPAN) before landing. I am wondering why he told me to stop using it??

[illusion]

Here is the FAR 25 reference regarding max alt and 8000' cabin.

Most transport category jets are capable of flying higher, however the limit is the 8000' cabin requirement . A higher pressure differential to mainmtain the 8000' at a higher altitude would require a higher pressure differential which would require a stronger/heavier sructure. AT 39,000' a diff of about 8.6 PSI is required.

http://edocket.access.gpo.gov/cfr_2003/pdf/14cfr25.841.pdf

[blueloo]

wondering why he told me to stop using it?

Because its easier to say no if you have no idea.


There is also a remote possibility that the Cabin Crew Ops Manual is not aligned with our manual (although this is very unlikely). As far as I am aware, our manual takes precedence.

[ZappBrannigan]

When I was on the a QF plane, a QF cabin crew told me to turn off the camera (it's a Group 1 device with no bluetooth and WPAN) before landing. I am wondering why he told me to stop using it??QF policy is no personal electronic devices during takeoff and landing, regardless of their transmitting capabilities. This is normally enforced prior to the seatbelt signs being initially turned off after departure, and after top of descent. Now and again I've seen the landing requirement enforced at the "prepare for landing" instruction but it's normally at ToD.

At other times, they'll generally allow anything that doesn't transmit. My experience with the business crowd is a large percentage simply ignore the instructions anyway - lots and lots of phones on Silent on every flight.

Edit: apologies, didn't read the last couple of pages properly, just read Blueloo's post. I agree with the above - some just aren't fully aware of the details.

[Keyser.Soze]

the true altitude displayed by the GPS (give or take some smallish errors) and the pressure altitude are the same if the QNH is 1013 AND the temperature profile of the air up to FL410, in this instance, is standard. otherwise they're not the same (which only happens all the time)

someone using a GPS in an airliner wouldnt bother me unless he was strapping a parachute on at the time or popping a full clip in his uzi or something