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Windowseater
Topic Author
Posts: 51
Joined: Mon Apr 17, 2006 6:22 pm

Flight Mode

Fri Jun 09, 2006 1:27 pm

Hello everyone !

Tried a search on this topic, but no result.

Some cellphones and PDAs have a flight mode wherein you can use them in-flight without being able to make calls/send SMSes.

Technically speaking, what goes off in the phone to be able to be in this mode ? Does a kind of signal circuit get disabled or something ?

Thanks in advance !
'To invent an airplane is nothing. To build one is something. To fly is everything.' - Otto Lilienthal
 
DC-10Tech
Posts: 291
Joined: Fri Jun 15, 2001 6:40 pm

RE: Flight Mode

Fri Jun 09, 2006 2:03 pm

My phone has 'airplane' mode and I'm sure that it simply shuts off the transmitter in the phone (and possibly the receiver as well).

If the phone isn't transmitting, it becomes just another electronic gadget like a walkman, laptop, etc.
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Newark777
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RE: Flight Mode

Fri Jun 09, 2006 2:03 pm

I think it's just to please FA's who don't know any better.  Wink

Harry
Why grab a Heine when you can grab a Busch?
 
kaddyuk
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Joined: Thu Nov 08, 2001 1:04 am

RE: Flight Mode

Fri Jun 09, 2006 3:07 pm

When a mobile phone or PDA with the ability to transmit looses signal, it will boost the signal finder more and more until it finds a signal.

The problem is that this signal could interfere with certain aircraft systems. However, aircraft should be protected against this type of interference because they fly through areas of intense interference at times.

Even using cellular devices without flight mode isn't dangerous as such. But better be safe than sorry...
Whoever said "laughter is the best medicine" never had Gonorrhea
 
Ralgha
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RE: Flight Mode

Fri Jun 09, 2006 3:58 pm

Quoting Kaddyuk (Reply 3):
The problem is that this signal could interfere with certain aircraft systems. However, aircraft should be protected against this type of interference because they fly through areas of intense interference at times.

Even using cellular devices without flight mode isn't dangerous as such. But better be safe than sorry...

The most common effect can be heard through the crew's audio systems. I've had cell phone interference to the point where I couldn't use the comm radios. Isn't dangerous huh?
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
 
ThirtyEcho
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RE: Flight Mode

Fri Jun 09, 2006 4:15 pm

Once again, cell users, the interior of an aircraft fuselage forms what is known as a Faraday Cage; in this structure, electronic devices transmit signals that bounce around within the confines of the fuselage and shift frequency as they bounce. There is no way to anticipate or predict how these spurious signals will manifest themselves. Your primary transmission might be perfectly benign but the second or third shift might mask an ILS signal, block a VOR signal or send an autopilot off chasing a phantom radial.

Private pilots use cells because they can restrict the use to non-critical phases of flight. Who cares, if you are VMC on top and in HDG mode or hand-flying, if the OBS needle bangs right or left when you call home?

Multiply the number of spurious signals in an airliner by the number of cells in use and you might get a couple of thousand different electronic flying monkees at any given time.

And the "given time" when this is most likely to happen is both on departure and on approach.
 
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HAWK21M
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RE: Flight Mode

Fri Jun 09, 2006 6:27 pm

Flight mode disables all radios (wifi,bt,cellular) in the pda. Rather than
shutting down each radio individually, chosing flight mode will do it in one
step.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
avioniker
Posts: 1100
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RE: Flight Mode

Fri Jun 09, 2006 9:59 pm

Let's not forget the internal bus on whatever device you happen to have "neglected" to turn off.
In a typical laptop computer the front end bus is 100 to 133Mhz. Unless you have the computer completely encased in a grounded shield some of that data gets transmitted into the surrounding environment at measurable levels.
Many portable devices use 8086 and 6505 processors which run and emit harmonics of the same frequencies.
Test question: Does anyone know why 100 to 133Mhz is a bad frequency to have bouncing around the aircraft?
And like Ralgha I've had trouble hearing ATL tower because of the number of people calling home to let them know they're almost there.
Just so we all understand the rules; here's the one that counts in the USA:

§ 121.306 Portable electronic devices.
(a) Except as provided in paragraph (b) of this section, no person may operate, nor may any operator or pilot in command of an aircraft allow the operation of, any portable electronic device on any U.S.-registered civil aircraft operating under this part.

(b) Paragraph (a) of this section does not apply to—

(1) Portable voice recorders;

(2) Hearing aids;

(3) Heart pacemakers;

(4) Electric shavers; or

(5) Any other portable electronic device that the part 119 certificate holder has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used.

(c) The determination required by paragraph (b)(5) of this section shall be made by that part 119 certificate holder operating the particular device to be used.

[Doc. No. FAA–1998–4954, 64 FR 1080, Jan. 7, 1999]
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
Grbld
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RE: Flight Mode

Sun Jun 11, 2006 10:53 am

Quite simply, in our aircraft, you are not allowed to use devices that contain antennas in any way at all during the entire flight. That includes phones that have a flight mode, and in all reality, every modern laptop.

Though chances are slim that the laptop's wireless systems will be on (unless you love having your battery run down twice as fast), it's virtually impossible for the cabin crew to see that you actually have your phone on flight mode, so just don't use it in flight.
 
greg3322
Posts: 222
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RE: Flight Mode

Sun Jun 11, 2006 11:12 am

Quoting ThirtyEcho (Reply 5):
Once again, cell users, the interior of an aircraft fuselage forms what is known as a Faraday Cage; in this structure, electronic devices transmit signals that bounce around within the confines of the fuselage and shift frequency as they bounce. There is no way to anticipate or predict how these spurious signals will manifest themselves. Your primary transmission might be perfectly benign but the second or third shift might mask an ILS signal, block a VOR signal or send an autopilot off chasing a phantom radial.

I guess the 787 won't have this issue?

Greg
 
DC-10Tech
Posts: 291
Joined: Fri Jun 15, 2001 6:40 pm

RE: Flight Mode

Mon Jun 12, 2006 5:12 pm

Quoting Avioniker (Reply 7):
100 to 133Mhz is a bad frequency to have bouncing around the aircraft?

Those freqs cover the entire VOR/LOC range and just about all of the VHF comm range as well.
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Starlionblue
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RE: Flight Mode

Mon Jun 12, 2006 8:55 pm

The assumption is that pax will know how to turn off the radios. My new Thinkpad T60p has an actual switch that turns all radios (Bluetooth, Edge, WiFi) off. However, on my old laptop I had to turn them off in the OS. I have seen so many people with the WiFi on on planes (there is an indicator light) it's not even funny.

Having worked in tech support I have a pretty good understanding of the technical savvy of the average user.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
captjetblast
Posts: 289
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RE: Flight Mode

Wed Jun 14, 2006 3:05 am

Nah nah nah.

When on a plane they tell you to turn your cell phones off, that's because once in the air, say, at 3000 ft and at the speed of the aircraft, your phone, better said, hundreds of mobile phones in the air, will hold and quit quickly from one ground antenna to another, so the mobile phones system on the ground will get crazy and collapse. Sometimes more than one antenna will be able to pick your phone, or maybe your phone will pick more than one antenna. At higher altitudes, there'll be no problem, your phones will be dead, with no contact with ground.

There's no way to interfere with systems on board, the frequencies in use in air navigation are pretty far from the ones in use by cell phones systems.

As for the Faraday Cage, that's not the way it works.
 
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Starlionblue
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RE: Flight Mode

Wed Jun 14, 2006 3:43 am

Quoting Captjetblast (Reply 12):
There's no way to interfere with systems on board, the frequencies in use in air navigation are pretty far from the ones in use by cell phones systems.

There's plenty of evidence for interference. You can even find articles on the Boeing website.

As for frequencies, you are assuming all devices work as advertised. This is by no means a given.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
SP90
Posts: 351
Joined: Wed May 24, 2006 12:39 am

RE: Flight Mode

Wed Jun 14, 2006 6:13 am

Quoting Captjetblast (Reply 12):
When on a plane they tell you to turn your cell phones off, that's because once in the air, say, at 3000 ft and at the speed of the aircraft, your phone, better said, hundreds of mobile phones in the air, will hold and quit quickly from one ground antenna to another, so the mobile phones system on the ground will get crazy and collapse. Sometimes more than one antenna will be able to pick your phone, or maybe your phone will pick more than one antenna. At higher altitudes, there'll be no problem, your phones will be dead, with no contact with ground.

GSM phones will never hold more than one timeslot at any given time. That is why GSM phone perform what is called a hard handoff, it has to vacate one timeslot before getting assigned another in a adjacent cell. If you pay attention you can actually hear the click as it happens. CDMA based phone will have established connections with multiple antennas during normal operations and they perform soft handovers. Think of soft handover like Tarzan swinging on the vines, he grabs the next one before letting go of the previous one right? Mobile phone technology is designed to work on bullet trains going full speed so during takeoff and landing phase of flight the speeds of the airplane and the trains are similar so should present no problem for the phone or the network. The handover rate will increase but it's not going to cause the network to "go crazy and collapse" as you say. If you use GPRS, EDGE or any of the data services, the data rate will certainly drop as the speed of the aircraft increase. The quoted maximum data rates are for stationary users in a relatively clean enviornment (low interference).

Edited: Spell Check

[Edited 2006-06-13 23:16:37]
 
captjetblast
Posts: 289
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RE: Flight Mode

Thu Jun 15, 2006 10:02 pm

To SP90 (and everybody):

"GSM phones will never hold more than one timeslot at any given time. That is why GSM phone perform what is called a hard handoff, it has to vacate one timeslot before getting assigned another in a adjacent cell."

Right, but you're missing a factor: you are well above the ground and travelling fast, not just on a bullet trait on the ground. Randomly and erraticaly, your cell phone will hold and release one timeslot after another, and, of course, multiply it by the hundreds of passengers using their cells while on the air, near a busy airports, with tens of planes below FL100 or so. The problem would arise once the planes reaches, say, 1000 ft and below 10000 ft aprox.

As for the interference: cell phones frequencies ara well far beyond those in use in an aircraft: 900-1000 MHz vs. 108-132 MHz, even considering armonics, which in turn loose power as they depart from central frequency. And the power of broadcast of the aircraft systems are powerful enough to make the tiny power of your cells seem nonsense. For the contrary, the ground cell networks broadcast are powerful, but not enough to doom a plane (it simply didn't happend).

Regards
 
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Starlionblue
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RE: Flight Mode

Thu Jun 15, 2006 11:32 pm

Quoting Captjetblast (Reply 15):

As for the interference: cell phones frequencies ara well far beyond those in use in an aircraft: 900-1000 MHz vs. 108-132 MHz, even considering armonics, which in turn loose power as they depart from central frequency. And the power of broadcast of the aircraft systems are powerful enough to make the tiny power of your cells seem nonsense. For the contrary, the ground cell networks broadcast are powerful, but not enough to doom a plane (it simply didn't happend).

Not enough to doom a plane perhaps, but there is plenty of evidence for interference with navigation and other systems.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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