Are we nearing a point where common technologies are starting to interfere with each other... 5

No we are well past that point. Engineering judgement is supposed to balance the conflicts. Your example is what happens when the uninformed make important decisions without asking the correct questions.

Bit of rumour and history.

Any telecoms types feel free to correct me.

In the 90's when GSM was kicking off there was a battle between the aviation regulators the radio freq authorities and the phone OEMs.

The aviation regulators wanted the phone OEMs to certify the phones for aviation use and pay for it. At the time it was Nokia and Ericsson. They said no we are not certify every handset, just to get one done would be a fortune and take months and we fully expect to have new models every 6 months.

The aviation regulators the went to the radio feds and they said nothing to do with us.

So they banned them on aircraft.

But in the mean while they changed the certification standards so aircraft are more radio hardened.

This C band Freq is actually used in 3-4 systems.

The rad alt data is used for low Viz approaches Cat 2 and cat 3. But it's also linked into terrain avoidance and traffic.

Now the problem the FAA has is that the USA uses alot of old aircraft that predate the certification change or they have grandfathered from older models. So John it is sort of related to MAX issues.

It's not going to effect a 787 or 777 but nobody has a clue about the MAX or NG.

The radio feds want the cash from the frequency sale. And have absolutely zero interest again with aviation issues. Which they see as the aviation regulators fault for not dealing with years ago. The 5G frequency was in white papers before 2000.

Airbus, Bombardier, embraer etc have all had the issue sorted years ago. Boeing I believe haven't due grandfathered certification rules.

Please don't take any of the above as fact, but it's what believe is what the issue is.

They basically have a choice of down grade the aircraft effected so they can't operate in less than 200ft cloud base or 550meters Viz. Or find some way of turning 5G off when the airport's go low Viz approaches. Or have 5G black areas around airport approaches.

It's a political hot potato. Because its billions of dollars industry that are clashing against each other.

If the FAA does nothing and a fatal accident occurs then all hell will let loose again.

To note the 5G band in Europe is 3.4-3.8 GHz

USA it's 3.7 to 4.2

The rad ALTs work at 4.2 to 4.4.

I don't have a clue who decided that 4.2-4.4 was for rad alt.

I think it was a UK invention which is why it fits in with the European frequency allocation.

Spend some time on short wave radio and you will be amazed at how many different applications use various bandwidths.
A lot of these are 'short range' applications that aren't supposed to interfere. But over time many of these have seen increases in efficiency and power and now they interfere a lot.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

The modern rad ALTs fire coded pulses and ignore everything else. Code changes every pulse and it's octo or hex.

And modern aircraft have 3 rad alts and then compare them and then throw up a flag that one has been pulled from the mix and as long as the last two agree you can continue. Once they disagree then you have to bin it unless you can see the runway. You can go with just one but then you can't do any approaches that require radalt.

But it may screw with other systems.

The Turkish crash in skipol is a prime example.

The 737 only has suprise suprise 2 rad ALTs. One went tits up and the autothrottle went into retard landing mode thinking it was at -8 ft and pulled the power to flight idle the pilot didn't spot it. And they stalled and crashed every one dead.

The old systems just use a straight squirt without any code so are much more vulnerable to getting confused.


The frequency clash though is the old GSM bun fight over 850 and 900 MHz.

I think the US didn't want rad alt to use that band. But by the time they jumped on the band wagon the rest of the world were using it. But it fitted nicely with European frequency allocation, it was in an awkward hole in the US taking up two blocks instead of 1. And they seem to be trying to use one of those blocks for 5G.

The bulk of the USA domestic fleet though is legacy aircraft types. 2 rad ALTs no coding.

It must effect Canada as well and south America. I think they are 850 GSM as well.

Sorry just looked at the books

It's a frequency modulated continuous wave radar not a pulse.

There is a code in there somewhere though I believe.

I don't need to know how it works to be honest. Just what to do if one or more fails.

A good presentation on the issue

blancolirio said:

5G C-Band Interference with Radar Altimeters in Aviation

Click to expand...

Really good presentation.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

FM CW is what we used to call a Radio altimeter, as opposed to Radar Altimeters which are pulsed devices. I think I saw my first random-pulsed Radalt in the late 1980s (that one frequency-hopped as well, just for fun).

The Radio Alts used a linear sweep on the transmit frequency, then mixed that with the return to provide a beat whose frequency depended linearly on the difference between the two frequencies, hence on the delay between transmit and receive and hence on altitude. Feeding that into a Frequency to Voltage converter allowed you to drive a meter. I always thought that was a really ingenious low-tech solution.

A.

I think they also have a Doppler function as well these days that feeds into the egpws for windshear.

But it's one of these systems that has been linked into multiple other things apart from it's primary job. But it's not really been touched.

The A3xx family apart from the A380 apparently is effected as well. They also only have 2 so no error Cheching or voting.

Among all of the technical issues that are raised, the most interesting to me right now are actually philosophical.

To the FCC, consequences of failure that drive reliability analysis are driven economically.
To the FAA, consequences of failure that drive reliability analysis are driven by fatalities.

The FCC's testimony to Congress has taken the stance that "there's never been a problem" which is probably true. So from their perspective the precautions they have already taken are adequate and justified.

The FAA disagrees, but not by disregarding the facts put forward by the FCC, but because the FAA isn't permitted to rely on "never been a problem". The aviation safety mentality does not allow for designers, engineers or pilots to ignore known risks. For example, the whole underlying failure in the 737 MCAS saga was "never been a problem" until is suddenly was. The FAA has a much higher standard of proof than the FCC, viewed in this perspective. The FAA has spent decades developing policy and analytical methods to find, quantify, and manage risks to a level unseen in most other industrial sectors.

The FAA doesn't have the deep pockets to pay for the in-flight testing needed to prove interference or non-interference, to their standard of evidence. The test program would be very costly, take a long time, and require specially-equipped aircraft to collect the data.

Complicating matters, unfortunately, is the economics between the two governmental agencies are drastically different. The FCC spectrum auctions are worth billions of dollars of revenue to the FCC. The FAA bears most of the cost of all major certification programs, to the tune of millions of dollars. Maybe the FAA can do some cost recovery on big programs, but that's it.

It's not a level playing field.

different red lines FAA is 1 in 1 million flights fatality rate which means one crash per year with 1 death in the USA airspace and the FCC can make it up as they go along and claim no data.

FCC gets shit loads of billions into the bank due license sales. And realistically its not their problem the rest of the world as said screw you to the radio alt frequency. And the FAA has had over 20 years warning in the matter.

BTW the rad alt freq will not change. End of and don't even thick it will happen. The rest of teh world which does have sep on the freqs everything works great and nobody cares that the local domestic is screwed for low viz.

I might add I have done 8 low vis approaches out of 18 in the last 7 days which required the rad alt to be operational and legal and we would not have landed without it. And if I didn't have that tick in the box it would have meant at least another 20 tons of fuel loaded. And thats only in the last 7 days.

FMCW should be tolerant of random noise (to it), since the frequency chirp is fairly unique

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list

Its the old no triple data source and no error voting tolerance aka 73& max.

On board they all run at different frequency's so if two disagree the system dies, three and they can pull the one that disagrees out the mix and we can continue downgraded to 2. We can actually currently (well we could on the Q400) do them with only one working and one tech with I think a 10 day limit to get it fixed. 10 MEL items are not mission critical.

Its more a fault tolerance issue than anything else. But you definitely don't want things to throw a wobbly at 50ft. They have various failure modes Fail passive, fail operational, failed. But these rely on a complete failure of one unit to down grade to a single data source. To my knowledge the problem is a data quality issue and no way of determining which one is correct.

The FCC has only authorized the C-band use for 5G up to 3.95GHz. The radars start at 4.2GHz. It's quite astonishing that they're so terrible they apparently can't work right with a 200MHz guard band. That's utterly atrocious filter performance, I'm surprised the FAA authorized such dodgy systems in the first place.

you have to remember that some of the rad alts are 1960's. And certified to 1960's standards.

They are certified and if they haven't changed them since they won't be recertified to modern standards.

The FAA though is throwing the teddy out the pram though and are banning even CAT 1 and RNP approaches which you can't autoland off and rad alt previously could be completely offline and you could still do them.

right a bit of googling

Apparently the collins ALT-50 rad alt is the main stay of rad-alts more than 15 years old. Which is a colossal fleet bracket in the USA.

After that date then they use the collins ALT 1000-4000 series mostly. The biz jets tend to use Honeywell but as the bulk of the domestic fleet is the issue I stopped there. 737 Ng uses Collins alt 50.

All the manuals are pay to view but there is coming up a few things dating about 1975. They won't have had any certification work done on them since because there is no update to the installation paperwork and approval from the FAA in the doc logs.

They can change them but that requires a TSO and will be over 150k per aircraft for a single and don't have a clue how much it would be for a dual installation plus TSO for Boeing. Wouldn't surprise me though if its over half a million per airframe.

I don't think Airbus use Collins. But the FAA won't want to say its only a collins issue which mainly effects Boeing so they are banning the approaches not the hardware.

I have a suspicion there is a FCC V FAA empire war going on and FAA banning approaches is hoping that the politicians over ride the FCC.

BBB

A lot on that list.