In the final seconds before the January 2025 midair collision near Washington National Airport, a 0.8-second microphone key from within the helicopter blocked the words “pass behind” in the controller’s instruction, so the crew never received them (NTSB, Chair Homendy Senate Testimony 2026). The same frequency carried 29 transmissions in the 2 minutes before the collision, which killed 67 people. In Europe, air-ground communication made up 37% of the top seven contributors to ATM occurrences reported in 2018-2022 (EUROCONTROL, EVAIR Safety Bulletin No 25 2024), and an FAA content analysis of en route radio traffic found a readback error in 4.0% of pilot readbacks (FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009). VHF AM voice is still the backbone of air traffic control, and like other safety-critical voice networks, such as the public safety land mobile radio systems now going digital, it is short of channels and time. This roundup covers the radio link between cockpit and controller; for the noise problem of the people working beside the aircraft, see our aviation ramp and ground crew noise statistics. We aggregated data from the NTSB, EUROCONTROL’s EVAIR reporting system, NASA’s Aviation Safety Reporting System, the FAA’s Data Comm program and Civil Aerospace Medical Institute, EASA, and peer-reviewed human-factors and speech-recognition research.
TL;DR
- A 0.8-second mic key blocked the “pass behind” instruction 17 seconds before the DCA midair (NTSB, Chair Homendy Senate Testimony 2026).
- A readback error appeared in 4.0% of en route pilot readbacks, while 81.2% of controller messages got a full readback (FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009).
- Between every hundredth and every sixteenth ATC communication may contain an error, based on studies from 1993 to 2008 (Zuluaga-Gomez et al., ATCO2 Lessons Learned, arXiv 2023).
- Air-ground communication made up 37% of the top seven contributors to ATM occurrences in 2018-2022 (EUROCONTROL, EVAIR Safety Bulletin No 25 2024).
- Prolonged loss of communication events rose from 42 in 2020 to 146 in 2022, then eased to 119 in 2024 (EUROCONTROL, EVAIR Safety Bulletin No 26 2026).
- NASA’s ASRS received 121,128 safety reports in 2025, an average of 485 per working day (NASA ASRS, Program Briefing 2026).
- 8.33 kHz spacing raises the 118-137 MHz airband from 760 to 2,280 voice channels (NBAA, 8.33 kHz Radio Requirement 2015).
- 88.7% of transport-type State (military and government) aircraft in Europe were 8.33 kHz equipped by 2020 (EUROCONTROL, 8.33 kHz Implementation Support 2026).
- The NTSB issued 50 safety recommendations after the DCA midair, 33 of them to the FAA (NTSB, DCA Midair Board Meeting Press Release 2026).
- Only 20% of 55 surveyed Korean pilots, controllers and trainees used the correct MAYDAY FUEL phrase (Yun and Choi, Korean J Aerosp Environ Med 2023).
- 41% of US en route air carrier traffic used Data Comm text clearances in October 2024 (FAA, NAC Data Comm Briefing December 2024).
- EU rules have required CPDLC for IFR flights above FL285 since 5 February 2020 (EASA, Datalink FAQ accessed 2026).
1. Readback and Hearback Errors: How Often the Loop Breaks
Every ATC clearance is meant to travel a closed loop: the controller speaks, the pilot reads the instruction back (the readback), and the controller listens to that readback to catch mistakes (the hearback). The best tape-based measurement of that loop is still an FAA Civil Aerospace Medical Institute study of 51 hours of real en route radio traffic from five US air route traffic control centers, recorded in 2006, covering 4,261 controller transmissions that carried an instruction. It found an outright readback error, a wrong number or word, in 4.0% of readbacks, but an omission, where the pilot simply left part of the message out, in 67.4% of them (FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009). Most recent available data: FAA CAMI, 2009 (recordings from 2006).
The pattern matters more than the totals. Omissions climb with message complexity and length, so the safety lever is how controllers package information, not just how carefully pilots listen; the study’s own advice was to limit transmissions to three aviation topics. Automated hearback is the next layer: DLR researchers set themselves a goal of detecting better than 50% of readback errors with false alarms below 10% (DLR, Helmke et al. ATM Seminar 2021), but recognition accuracy on noisy, accented radio speech remains the bottleneck, a problem we track in our speech recognition accent bias statistics.
| Metric | Value | Source |
|---|---|---|
| Controller messages that received a full readback / a partial readback / no pilot acknowledgment (en route, 2006 sample; full readbacks were 71% in the 1993 comparison study) | 81.2% / 8.6% / about 3.8% | FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009 |
| Pilot readbacks containing a readback error (wrong value), 151 transmissions | 4.0% | FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009 |
| Readbacks classified as faulty in any way / with omission errors only | 71.3% / 67.4% | FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009 |
| Correlation of omission errors with message complexity / with message length | r = .46 / r = .29 | FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009 |
| Share of ATC communications that may contain an error (studies from 1993 to 2008) | Between 1 in 100 and 1 in 16 | Zuluaga-Gomez et al., ATCO2 Lessons Learned, arXiv 2023 |
| Pilot readback errors that controllers are able to detect (study from 1993) | Up to 90% | Zuluaga-Gomez et al., ATCO2 Lessons Learned, arXiv 2023 |
| Share of the cockpit contribution to European ATM incidents that comes from pilot action after a readback | About 40% | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
Context: the most common readback error topics in the 2006 sample were altitudes and altitude restrictions, followed by radio frequencies, route and position, and altimeter settings. In Europe, “hear-back omitted” was the most reported operational communication problem in 2024.
2. How Often Communication Shows Up in Safety Reporting Systems
Safety reporting systems do not measure how often things go wrong, only how often people choose to tell someone, so their totals are a floor. Even so, communication keeps rising to the top. Air-ground communication accounted for 37% of the top seven contributors to ATM occurrences reported to EUROCONTROL’s voluntary system between 2018 and 2022 (EUROCONTROL, EVAIR Safety Bulletin No 25 2024). The newer bulletin measures differently, against every ATM-related factor rather than the top seven, which is why its share is much smaller.
On the US side, NASA’s Aviation Safety Reporting System (ASRS), the confidential reporting program pilots and controllers use, is busier than at any point in the 2016-2025 series of its own briefing. Intake reached 131,138 reports in 2024 and stayed above 120,000 in 2025, a 7.6% dip (121,128 / 131,138 = 0.924) from the record (NASA ASRS, Program Briefing 2026). ATC procedures are one of the five most frequent subjects of the safety alerts ASRS sends to the FAA and industry.
| Metric | Value | Source |
|---|---|---|
| Air-ground communication share of the top seven contributors to European ATM occurrences (2018-2022) | 37% | EUROCONTROL, EVAIR Safety Bulletin No 25 2024 |
| Air-ground communication share of all ATM-related occurrence factors / of runway incursion contributory factors (2023-2024) | 7% / 13% | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
| ASRS reports received in 2025 (average per month / per working day) | 121,128 (10,094 / 485) | NASA ASRS, Program Briefing 2026 |
| ASRS reports received in 2024, the highest year in the 2016-2025 series | 131,138 | NASA ASRS, Program Briefing 2026 |
| Total ASRS reports received, April 1976 to December 2025 | 2,321,050 | NASA ASRS, Program Briefing 2026 |
| ASRS safety alert messages issued, April 1976 to December 2025 | 8,069 | NASA ASRS, Program Briefing 2026 |
| ASRS safety alerts on ATC procedures, January 2016 to December 2025 (fifth most frequent subject) | 163 | NASA ASRS, Program Briefing 2026 |
Context: ASRS does not verify or validate reports, and the briefing does not break its intake down by communication problem, so the US totals show the size of the reporting pipeline rather than the share that involves radio.
3. Call Sign Confusion and Prolonged Loss of Communication
Two failure modes sit at opposite ends of the radio problem. Call sign confusion happens when two flights with similar identifiers, such as consecutive flight numbers, share a frequency and one crew takes the other’s clearance. Prolonged loss of communication (PLOC) is the reverse: the aircraft stops answering the controller for an extended period. The number of airlines reporting call sign similarity or confusion to EUROCONTROL more than doubled, from 74 in 2020 to 163 in 2024 (EUROCONTROL, EVAIR Safety Bulletin No 26 2026), which says as much about wider participation in the reporting scheme as about the risk itself.
PLOC is the more expensive failure, because a silent airliner in European airspace can trigger a military interception. The event count rose with the traffic recovery after COVID, peaked in 2022 and has fallen since, both in absolute numbers and per 10,000 flights.
| Metric | Value | Source |
|---|---|---|
| Airlines reporting call sign similarity or confusion to EVAIR, 2020 vs 2024 | 74 vs 163 | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
| Call sign confusion instances reported to EVAIR, 2018-2022 | More than 800 | EUROCONTROL, EVAIR Safety Bulletin No 25 2024 |
| PLOC events reported in 2020 / 2022 / 2024 (rate per 10,000 flights) | 42 (0.08) / 146 (0.18) / 119 (0.11) | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
| Share of PLOC events in the en-route phase / approach phase (2020-2024) | 81% / 12% | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
| Share of PLOC events that ended in a military interception | About 6% | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
| Pilot responses using the complete / partial / an incorrect call sign (US en route, 2006 sample) | 74.5% / 14.5% / 1.3% | FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009 |
Context: incorrect pilot readbacks and frequency change errors are among the factors EUROCONTROL lists behind the PLOC events that led to interceptions. The bulletin also reports an overall increase in call sign confusion events in 2024, larger where the two flights belong to different airlines.
4. Frequency Congestion and the 8.33 kHz Channel Spacing Transition
Aviation voice radio uses amplitude modulation (AM) in a narrow slice of the VHF band, and only one person can talk on a channel at a time. Europe ran out of room first. Narrowing channel spacing from 25 kHz to 8.33 kHz expands the 118 to 137 MHz airband from 760 channels to 2,280, and without that change Europe was projected to be about 30 percent short of its future frequency needs (NBAA, 8.33 kHz Radio Requirement 2015). Most recent available data: NBAA, 2015.
The transition took nearly two decades, from upper airspace in 1999 to all radios operated in Europe by the end of 2017, and the long tail was State aircraft (EUROCONTROL, 8.33 kHz Implementation Support 2026). Extra channels only solve part of the problem, though: a single busy frequency still saturates. The NTSB’s analysis of the DCA midair shows how quickly a tower frequency fills, and it found that keeping helicopters on a separate frequency while one controller worked both meant pilots could not hear each other, which decreased situation awareness (Finding 47 of the NTSB final report, as presented in the testimony cited in the table below).
| Metric | Value | Source |
|---|---|---|
| VHF voice channels in the 118-137 MHz airband at 25 kHz vs 8.33 kHz spacing | 760 vs 2,280 | NBAA, 8.33 kHz Radio Requirement 2015 |
| Projected European frequency shortfall without 8.33 kHz | About 30% | NBAA, 8.33 kHz Radio Requirement 2015 |
| Deadline for all aircraft radios operated in Europe to be 8.33 kHz capable / end of sales of non-capable radios | December 31, 2017 / November 2013 | NBAA, 8.33 kHz Radio Requirement 2015 |
| States in the ICAO EUR region that mandated 8.33 kHz radios above FL245 (about 24,500 feet) in 1999 | Some 30 | EUROCONTROL, 8.33 kHz Implementation Support 2026 |
| Transport-type State (military and government) aircraft equipped with 8.33 kHz radios by 2020 | 88.7% | EUROCONTROL, 8.33 kHz Implementation Support 2026 |
| Radio transmissions on the DCA local controller’s frequency in the 2 minutes before the collision | 29 | NTSB, Chair Homendy Senate Testimony 2026 |
| Aircraft handled by the combined local and helicopter controller in the final 20 minutes (count about 90 seconds before the collision) | 7 to 12 (12) | NTSB, Chair Homendy Senate Testimony 2026 |
Context: EUROCONTROL’s implementation page also covers the 136.700 to 136.975 MHz band used for VHF data link (VDL), so data link takes its own slice of the same band, which is why voice offload (see section 7) and spectrum planning are linked.
5. Blocked Transmissions and Stuck Microphones
A blocked transmission, often called being “stepped on”, happens when two stations press their push-to-talk buttons at once: VHF radio cannot carry simultaneous transmissions, so part of a message is lost. A stuck microphone, where the push-to-talk switch stays engaged, keeps blocking the frequency until someone notices. The NTSB found that there is currently no system in use that lets controllers know when a simultaneous broadcast has occurred, and only one manufacturer has received an FAA design approval under the TSO-C122 simultaneous transmission standard since 1994 (NTSB, Chair Homendy Senate Testimony 2026).
The DCA midair turned that gap into a finding. Blocked transmissions prevented critical instructions from being fully received, and the board asked the FAA to implement anti-blocking technology that alerts controllers or crews to potentially blocked transmissions (NTSB, DCA Midair Board Meeting Press Release 2026). The congestion figures in section 4 explain why overlap was likely on that frequency.
| Metric | Value | Source |
|---|---|---|
| Length of the helicopter mic key that blocked “pass behind” / time before the collision | 0.8 seconds / 17 seconds | NTSB, Chair Homendy Senate Testimony 2026 |
| Manufacturers with an FAA TSO-C122 (simultaneous transmission) design approval since 1994 | 1 | NTSB, Chair Homendy Senate Testimony 2026 |
| Systems in use that tell controllers a simultaneous broadcast has occurred | None | NTSB, Chair Homendy Senate Testimony 2026 |
| Findings / safety recommendations approved in the DCA midair investigation | 74 / 50 | NTSB, DCA Midair Board Meeting Press Release 2026 |
| Recommendations addressed to the FAA / to the US Army | 33 / 8 | NTSB, DCA Midair Board Meeting Press Release 2026 |
| Seconds before the collision that an airborne ADS-B In traffic system could have given the airliner crew its first alert | 59 | NTSB, DCA Midair Board Meeting Press Release 2026 |
Context: the FAA’s TSO-C128 standard covers stuck microphones on the aircraft side. In July 2025 the FAA withdrew its plan to cancel TSO-C122a and reopened the comment period.
6. Phraseology and ICAO Language Proficiency
Standard phraseology exists so that a clearance means the same thing in Seoul, Sao Paulo and Seattle, and ICAO’s language proficiency requirements back it with a test. The international floor is ICAO Operational Level 4, and the FAA applies the same minimum to all FAA-certificated airmen (FAA, AC 60-28B English Language Standard 2017). Passing the test does not guarantee that people use the exact words, especially for rare phrases. In a 2023 Korean survey of 55 pilots, controllers and trainees, only 20% chose the correct MAYDAY FUEL declaration for a fuel emergency; 47% said “declaring emergency” and 33% said “minimum fuel” (Yun and Choi, Korean J Aerosp Environ Med 2023).
That gap is the real story behind language proficiency: everyday phrases are well practised, while the phrases reserved for emergencies, the ones a crew may say once in a career, are the ones people get wrong. In Europe, EUROCONTROL reports that non-standard phraseology rose after COVID and returned to pre-pandemic levels by 2024, and it lists language and accent as a category of spoken communication problems.
| Metric | Value | Source |
|---|---|---|
| Minimum ICAO English level for international radiotelephony and FAA-certificated airmen | Level 4 (Operational) | FAA, AC 60-28B English Language Standard 2017 |
| Skill areas rated in an ICAO language proficiency assessment | 6 (pronunciation, structure, vocabulary, fluency, comprehension, interactions) | FAA, AC 60-28B English Language Standard 2017 |
| Average score on an 8-item standard phraseology test, Korean survey of 55 pilots, controllers and trainees | 3.67 of 8 | Yun and Choi, Korean J Aerosp Environ Med 2023 |
| Respondents who chose the correct MAYDAY FUEL declaration | 20% | Yun and Choi, Korean J Aerosp Environ Med 2023 |
| Respondents who phrased a descent to 2,000 feet correctly | 18% | Yun and Choi, Korean J Aerosp Environ Med 2023 |
| Respondents who phrased “expect further clearance” with the correct preposition | 24% | Yun and Choi, Korean J Aerosp Environ Med 2023 |
| Respondents who included “of” in “hold short of runway” | 73% | Yun and Choi, Korean J Aerosp Environ Med 2023 |
Context: the Korean survey is small and scored written answers, not recorded radio traffic, and the authors note an internal inconsistency in how they report the score distribution. Treat it as an indicator of where phraseology knowledge is thin, not as a national rate.
7. CPDLC Data Link as a Voice Offload
Controller-pilot data link communications (CPDLC) move routine clearances off the voice channel and onto text messages that appear on a cockpit display, with no readback to mishear. In the US the FAA calls its program Data Comm. By October 2024, 41% of en route air carrier traffic in the US used Data Comm, and the number of equipped aircraft rose 65% to 8,707 (FAA, NAC Data Comm Briefing December 2024). The question is no longer whether text works, but how fast the rest of the fleet and the remaining centers catch up.
The FAA reports two benefit blocks for its tower departure clearance and en route services. Added together, they total more than 13.15 million minutes of radio time saved (5.95M+ plus 7.2M+), about 219,000 hours or 25 years of continuous transmission (13,150,000 / 60 = 219,167 hours; / 8,760 = 25.0 years), and more than 2.1 million readback errors prevented (316,570+ plus 1.8M+). Those benefit figures are the FAA’s own modelled estimates, not counted incidents. Europe went further by rule: CPDLC has been mandatory above FL285 since 2020 (EASA, Datalink FAQ accessed 2026). The shift from voice to text mirrors other critical services, such as text-to-911 alongside voice calls.
| Metric | Value | Source |
|---|---|---|
| Share of US en route air carrier traffic using Data Comm (October 2024) | 41% | FAA, NAC Data Comm Briefing December 2024 |
| Aircraft equipped for US en route Data Comm (increase) | 8,707 (+65%) | FAA, NAC Data Comm Briefing December 2024 |
| US airports with Data Comm departure clearances / en route centers operating 24/7 | 65 / 17 | FAA, NAC Data Comm Briefing December 2024 |
| Radio time saved, departure clearance and en route services combined (FAA estimate) | More than 13.15 million minutes | FAA, NAC Data Comm Briefing December 2024 |
| Readback errors prevented, both services combined (FAA estimate) | More than 2.1 million | FAA, NAC Data Comm Briefing December 2024 |
| EU CPDLC mandate start date and floor for IFR flights in the regulated airspace | 5 February 2020, above FL285 | EASA, Datalink FAQ accessed 2026 |
Context: in Europe, CPDLC runs over ATN VDL Mode 2, and EUROCONTROL lists CPDLC failures among the most frequent effects of GNSS (satellite navigation) outages, so data link adds its own failure modes alongside voice rather than replacing it.
Summary: Air Traffic Control Radio Communication by the Numbers
| Metric | Value | Source |
|---|---|---|
| Length of the mic key that blocked “pass behind” before the DCA midair | 0.8 seconds | NTSB, Chair Homendy Senate Testimony 2026 |
| Transmissions on the DCA local frequency in the final 2 minutes | 29 | NTSB, Chair Homendy Senate Testimony 2026 |
| Fatalities / NTSB safety recommendations, DCA midair | 67 / 50 | NTSB, DCA Midair Board Meeting Press Release 2026 |
| Pilot readbacks containing a readback error (US en route, 2006 sample) | 4.0% | FAA CAMI, Prinzo et al. DOT/FAA/AM-09/2 2009 |
| Share of ATC communications that may contain an error (studies from 1993 to 2008) | Between 1 in 100 and 1 in 16 | Zuluaga-Gomez et al., ATCO2 Lessons Learned, arXiv 2023 |
| Pilot readback errors controllers are able to detect (1993 study) | Up to 90% | Zuluaga-Gomez et al., ATCO2 Lessons Learned, arXiv 2023 |
| Air-ground communication share of the top seven ATM occurrence contributors (Europe, 2018-2022) | 37% | EUROCONTROL, EVAIR Safety Bulletin No 25 2024 |
| Call sign confusion instances reported to EVAIR, 2018-2022 | More than 800 | EUROCONTROL, EVAIR Safety Bulletin No 25 2024 |
| PLOC events reported in Europe, 2024 (rate per 10,000 flights) | 119 (0.11) | EUROCONTROL, EVAIR Safety Bulletin No 26 2026 |
| ASRS reports received in 2025 | 121,128 | NASA ASRS, Program Briefing 2026 |
| Total ASRS reports, April 1976 to December 2025 | 2,321,050 | NASA ASRS, Program Briefing 2026 |
| VHF airband voice channels at 25 kHz vs 8.33 kHz spacing | 760 vs 2,280 | NBAA, 8.33 kHz Radio Requirement 2015 |
| European States that mandated 8.33 kHz radios above FL245 in 1999 | Some 30 | EUROCONTROL, 8.33 kHz Implementation Support 2026 |
| Correct MAYDAY FUEL declarations, Korean survey of 55 respondents | 20% | Yun and Choi, Korean J Aerosp Environ Med 2023 |
| Minimum ICAO English proficiency level for international radiotelephony | Level 4 | FAA, AC 60-28B English Language Standard 2017 |
| US en route air carrier traffic using Data Comm, October 2024 | 41% | FAA, NAC Data Comm Briefing December 2024 |
| Radio time saved by US Data Comm, both services combined (FAA estimate) | More than 13.15 million minutes | FAA, NAC Data Comm Briefing December 2024 |
| EU CPDLC mandate in force since | 5 February 2020 (above FL285) | EASA, Datalink FAQ accessed 2026 |
Methodology and Sources
We prioritized primary sources: accident investigation records, regulator and air navigation service provider reports, official reporting system data, and peer-reviewed research. Where the best measurement is older than three years, the section says so. No VoxBooster data is used.
- NTSB, Chair Homendy Senate Testimony on the DCA Midair Final Report, February 2026: blocked transmissions, frequency load, staffing and anti-blocking technology.
- NTSB, Systemic Failures Led to Midair Collision Over Potomac River, press release, January 2026: findings, recommendations, fatalities and ADS-B In timing.
- EUROCONTROL, EVAIR Safety Bulletin No 26 (2020-2024 data), May 2026: PLOC, call sign similarity and confusion, contributory factors.
- EUROCONTROL, EVAIR Safety Bulletin No 25 (2018-2022 data), May 2024: air-ground communication share and call sign confusion count.
- NASA ASRS, Program Briefing (data through December 2025): report intake and safety alert subjects.
- FAA Civil Aerospace Medical Institute, Prinzo, Hendrix and Hendrix, The Outcome of ATC Message Length and Complexity on En Route Pilot Readback Performance, DOT/FAA/AM-09/2, January 2009: readback, omission and call sign measurements.
- Zuluaga-Gomez et al., Lessons Learned in ATCO2: 5000 hours of Air Traffic Control Communications, arXiv 2023: summary of earlier communication error research and speech recognition word error rates.
- DLR, Helmke et al., Readback Error Detection by Automatic Speech Recognition to Increase ATM Safety, ATM Seminar 2021: detection and false alarm targets.
- NBAA, Most Business Aircraft Prepared for Upcoming 8.33 kHz Radio Requirement in Europe, April 2015: channel counts, projected shortfall and mandate dates.
- EUROCONTROL, 8.33 kHz Implementation Support: 1999 mandate and State aircraft equipage.
- FAA, Advisory Circular 60-28B, English Language Standard, June 2017: ICAO Level 4 and the six rated skills.
- Yun and Choi, A Study on Non-Compliance with Standard Phraseology and Communication Errors in Pilot-Controller Communication, Korean Journal of Aerospace and Environmental Medicine, September 2023: phraseology survey.
- FAA, NextGen Advisory Committee Data Comm Briefing, December 2024: usage, equipage and benefit estimates.
- EASA, Datalink FAQ: EU CPDLC mandate scope and date.
- Data watch: (1) EVAIR’s 37% (Bulletin 25) and 7% (Bulletin 26) shares for air-ground communication are not a trend: the first is a share of the top seven contributors, the second a share of all ATM-related factors. (2) EVAIR PLOC rates per 10,000 flights are read from a chart in Bulletin 26; the 2021 rate printed alongside 63 events (0.18) does not sit well with the 2022 rate for 146 events, so we cite only 2020, 2022 and 2024. (3) The FAA December 2024 briefing lists its departure clearance and en route benefit blocks without clear labels in the text layer, so we report only combined totals with the arithmetic shown; the FAA’s August 2022 briefing showed smaller cumulative totals, consistent with growth. These are FAA modelled estimates. (4) The tape-based readback figures date from 1993 to 2008, the most recent available; no newer large-scale recording study was found. (5) The Korean phraseology survey has 55 respondents and an internal inconsistency in its score distribution. (6) The FAA briefing targeted initial en route services at all continental US centers for 2Q2025 and full services for 3Q2026, so the 17-center figure is expected to rise. (7) We could not reach the full JTSB interim report on the January 2024 Haneda runway collision or the ICAO language proficiency implementation surveys, so neither is quantified here.
Last updated: October 24, 2026. We update this roundup quarterly, and the next refresh is expected when EUROCONTROL publishes EVAIR Safety Bulletin No 27 and the FAA presents its next NextGen Advisory Committee Data Comm update.