Airborne satnav

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Graham_Wright

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I find it interesting to view my position on my Navman satnav when travelling as a passenger on a commercial flight. In particular, it is amusing when the message "Warning, you are exceeding 500 mph" appears. It aids recognition of ground features which provides some in-flight entertainment.

I have been told by cabin crew once to switch it off when taking off or landing and once during the flight. At the same time, other electronic gizmos are used throughout the flight and even childrens' elcronic toys during the take-off and landing without reprimand.

My understanding is that a satnav position fixing device is in essence a radio receiver. It presumably generates no more electronic noise than other computer devices.

Whilst obviously not wishing to prejudice the operation of the aircraft's instruments, as an ex-airborne systems engineer, I cannot understand the restriction.

Can any other forumites confound this belief?
 
On the basis that presumably the aircraft has one, I assume they don't turn theirs off during take off and landing.

afaik a satnat does not produce ant more noise that a radio, otherwise it would interfere with other kit on a boat, car, plane etc.
 
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On the basis that presumably the aircraft has one, I assume they don't turn theirs off during take off and landing.

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I suppose you could assume that their satnav would be screened against emissions like other equipment. But, good point!
 
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It presumably generates no more electronic noise than other computer devices.


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Quite. "Presumably".

The reason you are asked to switch things off during critical phases of flight (and not use cellphones at all) is because they just don't know what effects they may have. Thre are so far no significant numbers of airliners that were designed since cellphones and computers became commonplace, and so few, if any aircraft are protected against stray wigglies. Almost every electronic device contains an oscillator of some sort that will emit some RF. The airline and aircraft manufacturer cannot know which device you have, they cannot tell what it emits, or in what form or direction. They cannot tell where in the cabin you will be using it, or which way it will be pointing - if it is a directional emitter. They cannot evaluate local foci of RF energy that may be created by reflections from the aircraft's structure. In short, there are so many squillions of variables that it is almost impossible to achieve known safety without a design-onwards approach to screening everything on board.

The electronics fitted to an aircraft are specifically designed for such a purpose, which is extremely costly. They then have to be certificated for use by the CAA, which is even more costly (talking several noughts for Commercial equipment) and then the installation has to be proven and certificated too. That way it is known to be safe, but at vast expense. (The landing light in a small Cessna is identical to an old fashioned tungsten filament automotive part. You can buy the same thing in an auto store for a few pence. Certificated for aviation use it will cost £25 or more. I don't think anyone has got round to halogen landing lamps in aircraft because the cost of certification is so astronomical that no profit would ever be made.)

You have heard the noise a phone makes if you put it near a radio or hi fi - imagine what the computers on an Airbus are going to make of such a random input into the flight control computer input cable, or the digital throttle control, or the flap position computer. Not a good plan, I think you will agree.

They ask for a good reason, because it may, just may. be hazardous. There have been accidents to airliners believed caused by emissions in the cabin, and many examples of interference with systems.

On a UK registered aircraft it is a criminal offence to fail to comply with a lawful command of the Captain, which being asked to switch off is, and failure to comply in this case could also be construed as hazarding the safety of an aircraft, a very serious offense indeed.

The police do get called to deal with those few who refuse to comply, who are arrested and usually recieve large fines or worse. The courts are often draconian and very much on the Airlines' side in such matters, as they should be.

Safety comes first in the air, as it does at sea. It's just that we take your safety very seriously indeed in the air, which is why air travel is so safe, but it does require the co-operation of the passengers too - emphasis on "require"...
 
MASH is quite right that you are suffering because most electronics have a microprocessor in them which has an oscilator and therefor potential to radiate and cause interference to navigation aids.
My computer that I am typing on creates a huge interference on HF but it is not supposed to radiate. The lower powered devices like GPS have less radiation but then who is going to test and discriminate between all the devices a passenger might carry on board. Just like rules on dangerous cargo.
Here in Oz the regulations do not speak to electronic devices only that you must do as the pilot says. The Authority leaves it to(and requires) the company to make appropriate regulations and enforce them. As there is of late a loosening of the regs about mobile phones I expect the rules on electronics to be loosened over time. (maybe).
but yes all the electronics fitted to an aircraft are rigorously tested for interaction one with another.
lastly I am surprised you could get a signal in the cabin of an aircraft with your GPS.
For the record the number of proven instances of passenger's electronics affecting an aircraft over the last 25 years are very few across the entire world jet fleet. (single digits)
olewill
 
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It presumably generates no more electronic noise than other computer devices.


[/ QUOTE ]

Quite. "Presumably".

The reason you are asked to switch things off during critical <span style="color:red">(no;- ALL)</span>phases of flight (and not use cellphones at all) is because they just don't know what effects they may have. Thre are so far no significant numbers of airliners that were designed since cellphones and computers became commonplace, and so few, if any aircraft are protected against stray wigglies. Almost every electronic device contains an oscillator of some sort that will emit some RF. The airline and aircraft manufacturer cannot know which device you have, they cannot tell what it emits, or in what form or direction. They cannot tell where in the cabin you will be using it, or which way it will be pointing - if it is a directional emitter. They cannot evaluate local foci of RF energy that may be created by reflections from the aircraft's structure. In short, there are so many squillions of variables that it is almost impossible to achieve known safety without a design-onwards approach to screening everything on board.

<span style="color:red"> So why permit laptops, portable video games (even these during take-off and landing)?</span>

The electronics fitted to an aircraft are specifically designed for such a purpose, which is extremely costly. They then have to be certificated for use by the CAA, which is even more costly (talking several noughts for Commercial equipment) and then the installation has to be proven and certificated too. That way it is known to be safe, but at vast expense. (The landing light in a small Cessna is identical to an old fashioned tungsten filament automotive part. You can buy the same thing in an auto store for a few pence. Certificated for aviation use it will cost £25 or more. I don't think anyone has got round to halogen landing lamps in aircraft because the cost of certification is so astronomical that no profit would ever be made.)

You have heard the noise a phone makes if you put it near a radio or hi fi - imagine what the computers on an Airbus are going to make of such a random input into the flight control computer input cable, or the digital throttle control, or the flap position computer. Not a good plan, I think you will agree.

<span style="color:red"> But a cellphone is an emitter.</span>

They ask for a good reason, because it may, just may. be hazardous. There have been accidents to airliners believed caused by emissions in the cabin, and many examples of interference with systems.

On a UK registered aircraft it is a criminal offence to fail to comply with a lawful command of the Captain, which being asked to switch off is, and failure to comply in this case could also be construed as hazarding the safety of an aircraft, a very serious offense indeed.

The police do get called to deal with those few who refuse to comply, who are arrested and usually recieve large fines or worse. The courts are often draconian and very much on the Airlines' side in such matters, as they should be.

Safety comes first in the air, as it does at sea. It's just that we take your safety very seriously indeed in the air, which is why air travel is so safe, but it does require the co-operation of the passengers too - emphasis on "require"...

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<span style="color:red">That all makes sense but completely ignores the points I make about other devices. A radio is permitted (audio output) but a satnav (=radio with visual output) is not. I have asked the airline to explain and they accept this argument. My question has been referred"upwards".</span>
 
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MASH is quite right that you are suffering because most electronics have a microprocessor in them which has an oscilator and therefor potential to radiate and cause interference to navigation aids.
My computer that I am typing on creates a huge interference on HF but it is not supposed to radiate. The lower powered devices like GPS have less radiation but then who is going to test and discriminate between all the devices a passenger might carry on board. Just like rules on dangerous cargo.
Here in Oz the regulations do not speak to electronic devices only that you must do as the pilot says. The Authority leaves it to(and requires) the company to make appropriate regulations and enforce them. As there is of late a loosening of the regs about mobile phones I expect the rules on electronics to be loosened over time. (maybe).
but yes all the electronics fitted to an aircraft are rigorously tested for interaction one with another.
lastly I am surprised you could get a signal in the cabin of an aircraft with your GPS.
For the record the number of proven instances of passenger's electronics affecting an aircraft over the last 25 years are very few across the entire world jet fleet. (single digits)
olewill

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Are laptops and electronic games not normally permitted on Oz aircraft then?

It does take a while to receive a signal presumably because of the speed of the aircraft but it does help in trying to identify ground features.
 
GW, laptops and games are not usually allowed during t/o and landing. As I said I believe all UK airlines ban that.

A cellphone is an emitter. Quite, that is why they are banned altogether. They are also, incedentally, specifically banned from use outside on the apron (walking to the aircraft) by passengers, but not by staff but may be used inside until the doors are shut unless refuelling is taking place. Quite why the authorities allow this illogical anomaly is beyond me. It should be, no phones between boarding gate and immigration.

I have to say that I don't think there is any reason to stop you using the satnav in flight, that sounds a bit over-zealous, but you have to remember that you are often dealing with relatively inexperienced youngsters as cabin crew.

There isn't necessarily 100% logic in this anyway - some airlines are talking about introducing airborne cellphone us in the cabin - via asatellite and at ruinous expense to you, but thats the point. If it makes money in a business with miniscule margins, then $$ is likely to override other concerns. Can you imagine the misery of a long flight stuffed in next to some @rse braying into a cellphone - it will cause air rage. It will also cause interference, but I fear that is not going to stop the likes of O'Leary if profit results.

Basically, it is a good idea to do as you are asked on an aeroplane, but don't expect a rational answer, especially on technical or policy matters, from the crew on the day. It just is.


Olewill, many, many, many more than single figures.
 
Hi MASH up to y2000 I was ione of a handfull of Avionics specialists with Civil Aviation Safety Authority (Australian equivalent of CAA or FAA)
and was aware of the reports from other authorities. My ongoing belief was that it was all a beat up though I would never buck the party line of conservatism. There were not the same restrictions on electronics in small aircraft primarily because the pilot was aware of the activities of each passenger but again no reports of interference in this area. Perhaps in this case they didn't bother to report just tell the passenger to turn it off.

To add to others comments. Of course low level flight is far more critical. Especially if you consider that instrument landing systems are connected directly to the autopilot in cat 3 case to take the aircraft to ground level. That is certainly no time for a glich. olewill
 
Perhaps they make you switch off and put away during takeoff and landing so the satnav does not become a high speed ballistic missile heading for the back of someone's cranium during a crash situation hmm.

Imagine the poor hearse drivers reaction when driving the unfortunately brained individual on his last ride, if a voice comes from the coffin saying "at the cemetary gates, turn left and you have reached your destination".
/forums/images/graemlins/grin.gif
 
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