Unheard or Misheard Clearances
 

Does every station on the same frequency or channel hear the same transmissions at the same time ?
Obviously the answer is NO!

However Voice Communication is still very important in giving Clearances and Instructions.

There are so many possible variables involved that Readbacks of Clearances are Required.
Yet Accidents are still happening due to Misheard or Unheard, Clearances or Instructions.

In follow up comments, I propose to list some of the many reasons for this.
Disclaimer
I am not a "Professional" Pilot, however I worked on Military Avionics during the 1980s and 1990s. I also have several hundred hours experience in flying Single Engine Piston, Sailplanes, SLMGs etc.
I have operated from many RAF airfields including Cosford, Kinloss, Marham, Wattisham, Colerne, Dishforth, Laarbruch, Bruggen, Guttersloh, Wyton, Halton, Bicester and many other places in the UK, Germany, Austria, and Cyprus.

Squelch Settings
Blocked or "Stepped On" transmissions.
Other calls on "Guard" frequency.
Language differences
Different makes and models of TX and RX
Distance from TX, line of sight between antennas.
Bandwidth of equipment, The VHF AM band was previously split into 360 channels, then 720, and now 760 or 2280 8.33 khz channels.
Old equipment may still be in use in some GA aircraft or Gliders.

And your point is?

Well if you ignore the possibiity of HF long path I'd say that there is a negligible difference in the time that receiving stations hear a transmission.

What should be done in order to prevent a False picture of what occurred in an accident, when one side in an investigation may claim that a Clearance was given, but that clearance was Misheard or Misinterpreted due to incorrect phraseology, difficult accent, poor use of English, or some other significant factor.

I am reluctant to mention one particular recent accident because many posts and comments are being removed or censored if they don't "toe the party line".

Is voice communications still the best way to give Clearances or Instructions ?
In the early days of aviation, Light Signals, Flags, Flares and other methods of giving orders were sometimes used.
Is it now time for a digital replacement for voice clearances, or certainly a visual backup system ?

Well CPDLC is being used a lot more commercially, and you have the conversation recorded for you to look at later. I think it will some time before voice comms are deprecated, though.

Aircraft VHF coms should have changed to single sideband suppressed carrier (SSB) mode a long time ago. Doubled transmission would be easy to read without the carrier beat tone.

Never going to happen though as too much amplitude modulation (AM) equipment to be replaced now. If it had happened 50 years ago we'd all be used to it now. It could also have been introduced when many transceivers had to be replaced for reduced channel spacing.

Seems to me that clearances should be sent digitally from the air traffic computer to the aircraft's computer. The aircraft knows where it is, modern airliners know where they're planned to be soon, and it would know where it's cleared to be. If the two don't match then it can sound a claxon, alert the dog to bite the pilot or some such. Similarly the air traffic side will know when two objects have been cleared into the same space.

It's not trivial to do, but it's something than can be rolled out incrementally over decades and doesn't require any expensive hardware changes.

Correct read-back acknowledgements of verbal instructions has stood the test of time. Where it falls down is when gash replies are made, such as “Yeah, we can do that”, or no reply at all. Too often I have heard this on the airwaves over a certain large continent. There sometimes seems to be a competition to out-gash other users.

Contrast that with the London FIR, which was always a joy after a long night’s slog.

Mog

It has a lot to do with discipline. After several days flying on the trot when tired or just doing the same routine over and over again people let standards slip and phraseology can become slack. Different operators are more pedantic than others in the maintenance of good RT discipline. Certainly cultural differences and other distractions make a difference, CPDLC is becoming more available, maybe even Scottish might cotton on to it at some point!

I think we all had nonspectacular RT...I've misheard a call and I've been stopped on the taxiway reading back the wrong clearance brain understood the clearance but my mouth was stuck on the wrong clearance..I've stepped on ATC toes too and got an " remain clear of the class delta" those errors were in my early formative days so I treated them like life's lessons and I felt that I had to do better...but as far as RT mistakes been there done that got the hat and t-shirt

It would require entirely new hardware throughout the entire network as none of the current ACARS/FANS/ATN/CPDLC networks over VHF, HF or SATCOM are encrypted as A) it would be ruinously expensive to do so and B) the signals would be slowed by the encryption and have potentially negative consequences for Required Surveillance Performance and Required Communications Performance in the SATCOM environment in particular.

For that reason alone there’s going to be a need for someone on the flight deck to read datalink clearances before executing them for a long, long time.

You're making it too hard. Just use the same comms mechanism as now with a preformatted message, including a signature. Same as BABS did for years.

You don't need new hardware, "just" a software update and all the certification that goes with it!

Since a modern CPU can do an AES message in less than a microsecond and even a cheap 10 year old microcontroller can do it in the blink of an eye performance doesn't feel like an issue. Especially when the alternative is voice.

Deeply frustrating in the USA where one controller is managing multiple frequencies, but they’re not band-boxed together. You’re constantly talking over other people and vice-versa but you don’t even know you’re doing it. It’s slightly better with CPDLC but ultimately US air traffic control is some of the worst in the world.

Add to this the utter refusal of most American pilots to use standard phraseology because it doesn’t sound cool, and it’s simply a case of when, not if.