HF transmissions

[LEM]

Back in the time everybody was told to avoid HF transmissions while refuelling on the ground.

A few years ago Chiefpilot told us this precaution is no longer necessary, as the modern equipment is totally different, no more valves (?), and so on, and a big debate arose.

So, are HF transmissions to be avoided while refuelling on modern aircrafts or not?
Thanks :confused:

[fruitloop]

Don't do it !!!If in doubt have a look where the HF antenna is and them walk away from it for 25- 50 metres (depending on transmitter)and then walk in a radius around the focal point(danger zone !!)Have a look at your radio ops licence regards refuelling !!!

[Golden Rivet]

-regardless of the type of HF Transceiver you are still transmiting a lot of RF energy.

Boeing 757/767 manual states

DO NOT OPERATE THE HF COMMUNICATIONS SYSTEM WHILE PERSONS REFUEL OR DEFUEL THE AIRPLANE. AN EXPLOSION CAN CAUSE INJURIES TO PERSONS AND DAMAGE TO THE AIRPLANE.

MAKE SURE PERSONNEL STAY A MINIMUM OF 6 FEET AWAY FROM THE VERTICAL STABILIZER WHEN THE HF SYSTEM TRANSMITS. RF ENERGY FROM THE HF COMMUNICATION ANTENNA CAN CAUSE INJURIES TO PERSONNEL.

[QAVION]

"A few years ago Chiefpilot told us this precaution is no longer necessary, as the modern equipment is totally different, no more valves (?), and so on, and a big debate arose."

Peak output power still remains roughly the same for HF USB transmissions, LEM (400Watts) on modern HF systems. It shouldn't make a difference how that power is generated (valves or transistors).

Proximity of wiring and antennae to fuelling systems may have some bearing on the issue (many Boeing aircraft now have the HF Antennae/Tuners in the tail) rather than in the wing/wingtips. However, although I've found the following hard to believe, I've been told that transmissions can cause pieces of lockwire in remote locations to heat up at resonant frequencies (Perhaps if this lockwire is exposed to fuel dripping from refuelling connectors you could have a problem).

I can't say I've never accidently tuned the HF during refuelling, but it's not something I would make a habit of intentionally doing.

Perhaps your Chiefpilot is thinking of Radar technology where the power output is a lot less?

Regards.
Q.

[comxtek]

The amount of energy generated is still great. I was on a B737NG which was on ground power yesterday during a test of the HF system. During my transmission, the overhead warning lights would all dim with each syllable!!!

[LEM]

That's what I answered him! Thanks God that guy is no longer in charge.... :}

[flt_lt_w_mitty]

LEM - I think we are all glad he has gone, but beware, I hear he still has 'friends' in place - and knows who you are! Be careful.

[Sheep Guts]

Well have to concurr with everyone dont do it.

HF Radios still give you a boot if you grab the antenna, regardles if it was oldvalve powered or modern transistorised output Power amplifier.

The RF energy emmited also can be picked up by other antenni ( anything piece of wire dental filling even)
in the immediate area, induce a voltage and discharge, causing you guessed it, a spark.

Youll notice that refuellers dont carry phones or Radios, or they shouldnt for this reason. Same reason for putting petrol in you car at the gas station, ( no cell phones).

When I was a techo in the RAAF, I serviced a multitude of different radios and everyone of them, when keyed, would trip the earth leakage circuit breakers power outlets, on the bench.

Food for thought

Regards
Sheep;) :ok:


P.S. During my training in the RAAF in LAVERTON VIC, we took a PRC-47 HF SET out bush and did some exersises. We used the conventional antenna inverted V and adjusted the wavelength. But we also used other objects. Like an old Barbwire fence and even a wet tree. Pretty robust stuff the old HF. Both execisises worked and we talked to our base in the School.