HF keying when refuelling represents fire hazard?
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Machinbird,
I'd say that is how urban legends are created ....
A fuel tank is still to a large extent a 'Faraday cage', so RF would not have such a major effect.
"I never saw that particular malfunction again. ".
Your remark, Occam's razor, Murphy's law, etc. would say, AFAIAK, that a causal link between the fuel system failure and the HF system does not exist....
Personally, I would think a link between fuel fire risks and RF is more or less a red herring.
Sparks and fuel, yes. RF and fuel, no.
I'm interested, which is why I 'subscribed' to this thread.
But so far, I've not seen any 'technologically sound' discussion.....
CJ
I'd say that is how urban legends are created ....
A fuel tank is still to a large extent a 'Faraday cage', so RF would not have such a major effect.
"I never saw that particular malfunction again. ".
Your remark, Occam's razor, Murphy's law, etc. would say, AFAIAK, that a causal link between the fuel system failure and the HF system does not exist....
Personally, I would think a link between fuel fire risks and RF is more or less a red herring.
Sparks and fuel, yes. RF and fuel, no.
I'm interested, which is why I 'subscribed' to this thread.
But so far, I've not seen any 'technologically sound' discussion.....
CJ
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Originally Posted by ChristianJ
I'd say that is how urban legends are created ....
A fuel tank is still to a large extent a 'Faraday cage', so RF would not have such a major effect.
A fuel tank is still to a large extent a 'Faraday cage', so RF would not have such a major effect.
The presence of strong RF fields could sometimes be verified by the sparks playing on the links of the tiedown chains at night.
You would think that the skin of the aircraft would form an effective Farraday cage, but if the length of a panel is similar to a wavelength being transmitted, some coupling could occur. These panels were bedded in a thin layer of conformal sealant that tended to isolate them from the underlying structure. Immediately below were wire bundles, sensors, control cables and things like that. Without doing actual measurements, I'd say, "Never say never."
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There is an IEEE paper on this subject available to members:
"An investigation was performed to study the potential for RF power radiated from portable electronic devices (PEDs) to create an arcing/sparking event within the fuel tank of a large transport aircraft. This paper describes the experimental methods used for measuring RF coupling to the fuel tank and fuel quantity indication system (FQIS) wiring from PED sources located in the passenger cabin. To allow comparison of voltage/current data obtained in a laboratory chamber FQIS installation to an actual aircraft FQIS installation, aircraft fuel tank RF reverberation characteristics were also measured. Results from the measurements, along with a survey of threats from typical intentional transmitting PEDs are presented. The resulting worst-case power coupled onto fuel tank FQIS wiring is derived. The same approach can be applied to measure RF coupling into various other aircraft systems" ISBN 0-7803-6395-7
"An investigation was performed to study the potential for RF power radiated from portable electronic devices (PEDs) to create an arcing/sparking event within the fuel tank of a large transport aircraft. This paper describes the experimental methods used for measuring RF coupling to the fuel tank and fuel quantity indication system (FQIS) wiring from PED sources located in the passenger cabin. To allow comparison of voltage/current data obtained in a laboratory chamber FQIS installation to an actual aircraft FQIS installation, aircraft fuel tank RF reverberation characteristics were also measured. Results from the measurements, along with a survey of threats from typical intentional transmitting PEDs are presented. The resulting worst-case power coupled onto fuel tank FQIS wiring is derived. The same approach can be applied to measure RF coupling into various other aircraft systems" ISBN 0-7803-6395-7
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Hi,
depending on the configuration of the transmitter <-> antenna construction, there are at least two hazards (as written above, just for clarification once more...)
1. Transmitted RF has a resonance frequency on a resonance wavelength.
(And some multipliers above and beyond that, their strength depends on the quality of the used gear, mainly...)
This transmitted RF is usually much higher when HF is used than in VHF/UHF applications. This has to do with the benefits of higher wattage in HF (the gain in the higher frequencies of VHF/UHF is not as large as in HF's frequency regions).
The transmitted RF does include very high voltages and very high currents. (Almost) never at the same place but ... see on (2) below :-)
RF will bring everything in (electrical and/or magnetic) resonance that fits its needs. If an HF radio transmits - for example - in the 20m wavelength region, there'll be resonance on every metallic object that is 5m long or a multiplier of this (this is a cruelly simplified explanation). There can be even resonance on shorter or longer objects due to special effects like electrical or magnetic shortening or increase in e. or m. length due to capacities etc.
The argument with the Faraday Cage is not valid when the RF is emitted by the refuelled object. It's thinkable that an HF transmitter sends on a fixed frequency and the wing which has a fixed resonance frequency is 'adjusted' by the fuel level (think of a fuel tank as a large capacitor with a very large distance between platters and then fill the capacitor with Jet A1... ;-) )
There are countless possibilities of resonating airframe, malfunctioning fuel pumps, high induction currents on the pumps' motors etc. - all created by a simple coincidence in resonance between your HF radio's frequency and ANY object on the airplane that resonates on this frequency.
2. There's no ideal antenna.
First, antennas are always imperfect. There's no practical antenna solution that transmits all of the HF energy as resonating HF. There's always some electricity 'left' due to a wandering standing wave. (SWR Standing Wave Ratio)
This electricity usually works as an antenna heater ;-)
If there's the slightest problem with the antenna, this current can become really significant (almost every HF problem is due to antenna related problems, aerial RF that is...) - imagine this current finding a way from the HF antenna to your fuel, finely vaporized whilst refilling your tanks with high pressure... all you need is ONE broken insulation or a 'high quality Seattle soldering' out of place... ;-)
3. Jet A1 is not Halon.
One has to differentiate between a puddle of Kerosene on the ground and finely vaporized K. in a fuel tank. The latter is by far more prone to a spontaneous adventure in exothermous reaction... ;-)
What I want to say:
Please don't be mindless. There may be only a slight possibility of an incident regarding HF with Kerosene or other fuels... BUT... it's really possible.
Personally, I would not jeopardize my career, my plane or the lives of the people involved for a simple 'I don't believe in that'.
Kind regards,
Peter
PS: Even if the fuel has no problem with your el cheapo HF with its crappy antenna on your multi million dollar airplane. Seeing your fuel specialist falling down his ladder with severe HF burns on his fingers won't make your day, believe me. These burns are nasty and painful as hell and they tend to take a long time to heal, similar to fluoric acid. Don't play at work!
depending on the configuration of the transmitter <-> antenna construction, there are at least two hazards (as written above, just for clarification once more...)
1. Transmitted RF has a resonance frequency on a resonance wavelength.
(And some multipliers above and beyond that, their strength depends on the quality of the used gear, mainly...)
This transmitted RF is usually much higher when HF is used than in VHF/UHF applications. This has to do with the benefits of higher wattage in HF (the gain in the higher frequencies of VHF/UHF is not as large as in HF's frequency regions).
The transmitted RF does include very high voltages and very high currents. (Almost) never at the same place but ... see on (2) below :-)
RF will bring everything in (electrical and/or magnetic) resonance that fits its needs. If an HF radio transmits - for example - in the 20m wavelength region, there'll be resonance on every metallic object that is 5m long or a multiplier of this (this is a cruelly simplified explanation). There can be even resonance on shorter or longer objects due to special effects like electrical or magnetic shortening or increase in e. or m. length due to capacities etc.
The argument with the Faraday Cage is not valid when the RF is emitted by the refuelled object. It's thinkable that an HF transmitter sends on a fixed frequency and the wing which has a fixed resonance frequency is 'adjusted' by the fuel level (think of a fuel tank as a large capacitor with a very large distance between platters and then fill the capacitor with Jet A1... ;-) )
There are countless possibilities of resonating airframe, malfunctioning fuel pumps, high induction currents on the pumps' motors etc. - all created by a simple coincidence in resonance between your HF radio's frequency and ANY object on the airplane that resonates on this frequency.
2. There's no ideal antenna.
First, antennas are always imperfect. There's no practical antenna solution that transmits all of the HF energy as resonating HF. There's always some electricity 'left' due to a wandering standing wave. (SWR Standing Wave Ratio)
This electricity usually works as an antenna heater ;-)
If there's the slightest problem with the antenna, this current can become really significant (almost every HF problem is due to antenna related problems, aerial RF that is...) - imagine this current finding a way from the HF antenna to your fuel, finely vaporized whilst refilling your tanks with high pressure... all you need is ONE broken insulation or a 'high quality Seattle soldering' out of place... ;-)
3. Jet A1 is not Halon.
One has to differentiate between a puddle of Kerosene on the ground and finely vaporized K. in a fuel tank. The latter is by far more prone to a spontaneous adventure in exothermous reaction... ;-)
What I want to say:
Please don't be mindless. There may be only a slight possibility of an incident regarding HF with Kerosene or other fuels... BUT... it's really possible.
Personally, I would not jeopardize my career, my plane or the lives of the people involved for a simple 'I don't believe in that'.
Kind regards,
Peter
PS: Even if the fuel has no problem with your el cheapo HF with its crappy antenna on your multi million dollar airplane. Seeing your fuel specialist falling down his ladder with severe HF burns on his fingers won't make your day, believe me. These burns are nasty and painful as hell and they tend to take a long time to heal, similar to fluoric acid. Don't play at work!
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Our airline prohibited us from HF transmissions while dumping for a very good reason. About the same reason you don't smoke a cigarette while fueling your car. You might get by with it your whole life and you might not.
The primary problem with HF transmission while refueling is the possibility of coupling a significant amount of energy (enough to produce a spark across a small gap) in some nearby metallic object.
The aircraft, antenna, tanks and wiring may be in perfect shape. All failure modes of these subsystems may have been accounted for and designed to prevent inadvertent ignition of fuel vapors. But the situation on the ground is uncontrollable. There is no easy way to test every object that may be present within the near field of the HF antenna while on the ground for its ability to couple some radiated energy during a transmission. And since the area around fuel dispensing operations is classified as hazardous, eliminating possible ignition sources may require the prevention of introducing RF and/or electrical energy into them.
The aircraft, antenna, tanks and wiring may be in perfect shape. All failure modes of these subsystems may have been accounted for and designed to prevent inadvertent ignition of fuel vapors. But the situation on the ground is uncontrollable. There is no easy way to test every object that may be present within the near field of the HF antenna while on the ground for its ability to couple some radiated energy during a transmission. And since the area around fuel dispensing operations is classified as hazardous, eliminating possible ignition sources may require the prevention of introducing RF and/or electrical energy into them.
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I thought it an issue with classic 747's as the couplers were out in the wing tip. (during fueling) seems they expect the possibility of leaking/exposed fuel. Can anyone document a fire caused by an HF key during fueling in the last 20-30 OK even 40 years?
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My expectation was that this was a policy written based on experience.
Sometimes we don't wait for things to blow up before we fix them.
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It may be due to some analysis as well. Having done a few failure modes and effects analysis in my time, its common for engineers to identify such modes, perhaps do a bit of testing and revise a design or establish operational guidelines to prevent an actual situation from arising. The ability of an HF transmission to cause a spark in a nearby structure may have been something they observed in a lab.
Sometimes we don't wait for things to blow up before we fix them
Sometimes we don't wait for things to blow up before we fix them
Q: How old are aircraft? How old is HF as used in aircraft and what was the wattage of the first systems?
Now like I said before I could understand this in a 742 with the couplers and ant in the wingtips but the same policy is followed on the MD-11 with couplers and ant in the tail under the #2 inlet... There is no nearby structure that a spark could ignite fuel from. I claim wives tail based on an experience of a Darwin award recipient many years ago.
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Just for the hell of it, look at the ammeter the time you hit the PTT on the HF. From memory, the ones I used took something like 30-40 amps. Quite where all that powers goes I'm not sure, but not all of it stays inside, so to speak.
PM
PM
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IGh,
The two examples you mention both were ESD, not RF effects.
As to the autothrottle certification problem you quoted... I suppose you've seen my 'tale' about Concorde, where during early flight tests the a/c 'wagged its tail' during HF transmissions.
On Concorde, the HF aerials were two large slots in the vertical fin (visible on photos of the British 002 prototype, because there they were not painted for some reason) and they set up enough HF currents in the tail structure to interfere with the signals from the autostab yaw rate gyros, which were also fitted in the tail. Cured with some simple filters in the signal wires.
Apologies for the slight TD.
CJ
The two examples you mention both were ESD, not RF effects.
As to the autothrottle certification problem you quoted... I suppose you've seen my 'tale' about Concorde, where during early flight tests the a/c 'wagged its tail' during HF transmissions.
On Concorde, the HF aerials were two large slots in the vertical fin (visible on photos of the British 002 prototype, because there they were not painted for some reason) and they set up enough HF currents in the tail structure to interfere with the signals from the autostab yaw rate gyros, which were also fitted in the tail. Cured with some simple filters in the signal wires.
Apologies for the slight TD.
CJ
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-- UA562 / 3May70 Boeing 727-100, N7027 UA ship # 7527, center fuel tank "exploded" during refueling. Parked on ramp, MSP, then number Gate 24. Wx: 53 deg F, wind 290/ 8. Fueling had been in progress for eight minutes when a LOUD sharp BANG sounded (like a fire cracker); fuel vapor and smoke seen ejected from Left Wing Tip near Tank Vent and fuel dump outlet [witnessed from outside by S/O, Oz mechanic, and the fueller]. Fueling was stopped; S/O disconnected electrical power from the buses, APU then was shutdown. Inspection: explosion in #2 Tank (center) ... presumed static discharge within #2 tank induced by presence of steel clamps and bolt assembly . . . Investigation revealed that fuellers at MSP used 450 gpm rate ... F/A's inside cabin were asked about the sound (explosion), but they perceived only a bump as if someone had hit the a/c with a belt-loader. ...
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RF (400 W PEP) risks
Hi,
noox89:
Will elaborate asap on interesting issue. For now:
1) Several factors to consider when estimating probabilities: Fuel type, Antenna type, Power output (maximum at LOUD voice), Aircraft type, Aircraft condition, Refueling equipt. and condition, Temp, Dew point, etc.
2) In general the probability to fuel ignition i consider very low (Jet A-1).
3) On mobile or HT's (VHF/UHF) their batteries could be dangerous. (e.g. LiPo). Not the RF due it's lower out power.
I operated HF (high power) mobile (land) since 1970 in practically all possible situations and configurations (testing different antennas) and would say: I would avoid to key PTT during (ground
) refueling. Only if necessary. But IMO the risk of fire (in general) is low.
I will comment (tech. aspects involved) like "parasitic resonance" of nearby structures.
The FCOM mentioned i understand as a standard to simply put chances at zero.
HF keying when refuelling represents fire hazard?
Interesting question and will have pleasure to comment the many aspects involved.
Mac
PS
Machinbird:
Would like to study a little bit on this case. Position of A/C in respect to nearby HF poles, HF power output (Certainly > 1KW), location of the probes, etc.
Structures may resonate and develop High Voltages (and flash)
PS2
On RF issues i remember the EA6B canopy (gold shielded) because the jamming antenna behind.
PS3
There is A LOT of myths in this issue. Even among EE. This is an "analog" field and the feeling of the technicians are decaying due the "digital age". Few people really has expertise on the issue. The comment of Avtrician certainly comes from an expert.
PS4
Type 1106: Maybe someone has more info? This Strategic transport used "long wire".
Let's look.
PS5
PS6
bubbers44
On "dumping", (jetisoning) a TACAMO (with it's 30,000 ft trailing wire) fed by the 5,000 ft "exciter" should not, indeed.
(200,000 Watts RF power )
noox89:
Will elaborate asap on interesting issue. For now:
1) Several factors to consider when estimating probabilities: Fuel type, Antenna type, Power output (maximum at LOUD voice), Aircraft type, Aircraft condition, Refueling equipt. and condition, Temp, Dew point, etc.
2) In general the probability to fuel ignition i consider very low (Jet A-1).
3) On mobile or HT's (VHF/UHF) their batteries could be dangerous. (e.g. LiPo). Not the RF due it's lower out power.
I operated HF (high power) mobile (land) since 1970 in practically all possible situations and configurations (testing different antennas) and would say: I would avoid to key PTT during (ground
) refueling. Only if necessary. But IMO the risk of fire (in general) is low.I will comment (tech. aspects involved) like "parasitic resonance" of nearby structures.
The FCOM mentioned i understand as a standard to simply put chances at zero.
HF keying when refuelling represents fire hazard?
Interesting question and will have pleasure to comment the many aspects involved.
Mac
PS
Machinbird:
Would like to study a little bit on this case. Position of A/C in respect to nearby HF poles, HF power output (Certainly > 1KW), location of the probes, etc.
The presence of strong RF fields could sometimes be verified by the sparks playing on the links of the tiedown chains at night.
PS2
On RF issues i remember the EA6B canopy (gold shielded) because the jamming antenna behind.
PS3
There is A LOT of myths in this issue. Even among EE. This is an "analog" field and the feeling of the technicians are decaying due the "digital age". Few people really has expertise on the issue. The comment of Avtrician certainly comes from an expert.
PS4
Type 1106: Maybe someone has more info? This Strategic transport used "long wire".
PS5
PS6
bubbers44
On "dumping", (jetisoning) a TACAMO (with it's 30,000 ft trailing wire) fed by the 5,000 ft "exciter" should not, indeed.
(200,000 Watts RF power )
Last edited by RR_NDB; 30th Mar 2012 at 16:27. Reason: typo
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Hi,
grounded27:
Amelia Earhart tried HF use (unsuccessfully) in her doomed flight in 1937. They were heard (IIRC, loud and clear) on Itasca (ship) but a probable aerial broked in Lae take off reduced drastically the ERP (effective radiated power) only allowing short distance comm.
I will study to trace the beginning of use of HF on A/C.
The capabilities of first Systems were very limited. They used CW (morse code) thus compensating equipt. limitations. Later on they introduced AM (phone) with limited performance due the use of AM (amplitude modulation. The same used currently used in VHF comm. today).
The power levels were low (due derated RF tubes to increase "TBO" MTBF). For example, the "powerful" Collins ART13 (extensively used in WW II) was rated 100 W only. I have a Bendix TA12 (a good equipt.) with just 40 Watts (AM) from WW II. The "Command Set" designed for gliders. used same power level.
With the introduction of SSB (an highly improved AM) the power levels went to the 400 w PEP (peak envelope power) standard today. Enough to you be heard by good operators in ground stations. (not always the case)
Based in my experience of ~ 5,000 hours of (land mobile) continuous HF use (SSB or CW/morse 500 W power level) i can say with a proper selection of frequency and with a good (efficient) antenna you have (most* of time) WORLD WIDE comm.
The problems faced in A/C using HF are to be commented later. Derives from several factors.
Mac
(*) With CW (Morse) ALL TIME: 99,99%,
grounded27:
How old is HF as used in aircraft and what was the wattage of the first systems?
Amelia Earhart tried HF use (unsuccessfully) in her doomed flight in 1937. They were heard (IIRC, loud and clear) on Itasca (ship) but a probable aerial broked in Lae take off reduced drastically the ERP (effective radiated power) only allowing short distance comm.
I will study to trace the beginning of use of HF on A/C.
The capabilities of first Systems were very limited. They used CW (morse code) thus compensating equipt. limitations. Later on they introduced AM (phone) with limited performance due the use of AM (amplitude modulation. The same used currently used in VHF comm. today).
The power levels were low (due derated RF tubes to increase "TBO" MTBF). For example, the "powerful" Collins ART13 (extensively used in WW II) was rated 100 W only. I have a Bendix TA12 (a good equipt.) with just 40 Watts (AM) from WW II. The "Command Set" designed for gliders. used same power level.
With the introduction of SSB (an highly improved AM) the power levels went to the 400 w PEP (peak envelope power) standard today. Enough to you be heard by good operators in ground stations. (not always the case
)Based in my experience of ~ 5,000 hours of (land mobile) continuous HF use (SSB or CW/morse 500 W power level) i can say with a proper selection of frequency and with a good (efficient) antenna you have (most* of time) WORLD WIDE comm.
The problems faced in A/C using HF are to be commented later. Derives from several factors.
Mac
(*) With CW (Morse) ALL TIME: 99,99%,
Last edited by RR_NDB; 31st Mar 2012 at 17:09. Reason: Add link
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Thank you for the good read RR_NDB! Google has failed me on this search. Actual events of danger during ground refueling still are not to be found but I much appreciate your post!
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Near field (RF)
Hi,
MB:
Was not the case because suspect would be HF through pole antennas. Specially if put vertical (few feet from A/C) and delivering high ERP (effective radiated power).
Do you remember on the use of frequencies near high end of HF spectrum? (30 MHz)
Another point. Certainly would not be caused by SSB or CW. Should be data. (duty cycle considerations-time duration of high power use)
Question: The probes suffered? Had to be replaced? Do you remember?
Mac
PS
The plane could act as a "path" to conduct RF amps (as a ground plane) above carrier deck.
Anyway, i consider unlikely RF caused the issue.
But i still don't discard the possibility.
PS
Which other reason could explain the facts (in TWO planes) Any other cause?
Or other possibilities should be discarded?
MB:
.. but if the length of a panel is similar to a wavelength being transmitted, some coupling could occur.
Was not the case because suspect would be HF through pole antennas. Specially if put vertical (few feet from A/C) and delivering high ERP (effective radiated power).
Do you remember on the use of frequencies near high end of HF spectrum? (30 MHz)
Another point. Certainly would not be caused by SSB or CW. Should be data. (duty cycle considerations-time duration of high power use)
Question: The probes suffered? Had to be replaced? Do you remember?
Mac
PS
The plane could act as a "path" to conduct RF amps (as a ground plane) above carrier deck.
Anyway, i consider unlikely RF caused the issue.
But i still don't discard the possibility.
PS
Which other reason could explain the facts (in TWO planes) Any other cause?
Or other possibilities should be discarded?
