A landing C172 is overtaken and almost hit on short final by another C172. Instructor pilot reporter...

Attributes
ACN	424281
Time
Date	199811
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lna
State Reference	FL
Altitude	agl bound lower : 150 agl bound upper : 150
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Flight Phase	landing other other
Route In Use	approach : visual
Flight Plan	None
Aircraft 2
Make Model Name	Skyhawk 172/Cutlass 172
Flight Phase	descent : approach other
Route In Use	approach : visual
Person 1
Affiliation	Other
Function	instruction : instructor oversight : pic
Qualification	pilot : cfi pilot : commercial pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 2000 flight time type : 700
ASRS Report	424281
Person 2
Affiliation	Other
Function	flight crew : single pilot instruction : trainee
Events
Anomaly	conflict : nmac non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	other
Miss Distance	horizontal : 25 vertical : 25
Supplementary
Air Traffic Incident	other

Narrative:

While on the final approach for runway 8R at the north palm beach county airport, the pilot of the other airplane frantically shouted on the unicom frequency that another airplane was in his way. I was instructing a student pilot on how to land the airplane and did not make an immediate reply. I looked both sides and in front but did not see the other airplane. We had extended our downwind to follow behind a twin piper which descended onto the downwind from a higher altitude. I can only surmise that the other C172 had flown a short pattern and had cut in front of us and made a steep descent which brought him over and behind our airplane. The pilot of the other cessna made a go around and was quite shaken up. Witnesses on the ground said the other airplane came within half a wingspan of ours on short final. Fortunately, my student was not aware of what had happened and he remained very calm. Although every airplane made position reports in the traffic pattern, the communications were frequently blocked by xmissions from airplanes at other airports using the same CTAF/unicom frequency of 123.0 MHZ. It is not uncommon to hear xmissions from several nearby airports using the same frequency. Wellington, a private field to the south, okeechobee (obe) and indiantown (X58) to the northwest, dade collier training facility to the south. On some days we hear xmissions from airports some 100 mi away, arthur dunn, naples and valkaria. Although aircraft communication radios are now required to have 720 channels, neither the FCC nor FAA has designated unicom/CTAF frequencys in the 0.05 and .25 MHZ intervals to relieve the congestion on the limited frequencys (122.7, 122.8, 122.9 and 123.0 MHZ) assigned to uncontrolled airports around the country. The equipment is in place. It is time to split up the frequencys to avoid congestion on the frequency for obvious safety reasons.

Original NASA ASRS Text

Title: A LNDG C172 IS OVERTAKEN AND ALMOST HIT ON SHORT FINAL BY ANOTHER C172. INSTRUCTOR PLT RPTR CITES THE FREQ OVERLAP FROM NEARBY ARPTS AS BLOCKING RADIO XMISSIONS OF ACFT IN THE TFC PATTERN.

Narrative: WHILE ON THE FINAL APCH FOR RWY 8R AT THE NORTH PALM BEACH COUNTY ARPT, THE PLT OF THE OTHER AIRPLANE FRANTICALLY SHOUTED ON THE UNICOM FREQ THAT ANOTHER AIRPLANE WAS IN HIS WAY. I WAS INSTRUCTING A STUDENT PLT ON HOW TO LAND THE AIRPLANE AND DID NOT MAKE AN IMMEDIATE REPLY. I LOOKED BOTH SIDES AND IN FRONT BUT DID NOT SEE THE OTHER AIRPLANE. WE HAD EXTENDED OUR DOWNWIND TO FOLLOW BEHIND A TWIN PIPER WHICH DSNDED ONTO THE DOWNWIND FROM A HIGHER ALT. I CAN ONLY SURMISE THAT THE OTHER C172 HAD FLOWN A SHORT PATTERN AND HAD CUT IN FRONT OF US AND MADE A STEEP DSCNT WHICH BROUGHT HIM OVER AND BEHIND OUR AIRPLANE. THE PLT OF THE OTHER CESSNA MADE A GAR AND WAS QUITE SHAKEN UP. WITNESSES ON THE GND SAID THE OTHER AIRPLANE CAME WITHIN HALF A WINGSPAN OF OURS ON SHORT FINAL. FORTUNATELY, MY STUDENT WAS NOT AWARE OF WHAT HAD HAPPENED AND HE REMAINED VERY CALM. ALTHOUGH EVERY AIRPLANE MADE POS RPTS IN THE TFC PATTERN, THE COMS WERE FREQUENTLY BLOCKED BY XMISSIONS FROM AIRPLANES AT OTHER ARPTS USING THE SAME CTAF/UNICOM FREQ OF 123.0 MHZ. IT IS NOT UNCOMMON TO HEAR XMISSIONS FROM SEVERAL NEARBY ARPTS USING THE SAME FREQ. WELLINGTON, A PVT FIELD TO THE S, OKEECHOBEE (OBE) AND INDIANTOWN (X58) TO THE NW, DADE COLLIER TRAINING FACILITY TO THE S. ON SOME DAYS WE HEAR XMISSIONS FROM ARPTS SOME 100 MI AWAY, ARTHUR DUNN, NAPLES AND VALKARIA. ALTHOUGH ACFT COM RADIOS ARE NOW REQUIRED TO HAVE 720 CHANNELS, NEITHER THE FCC NOR FAA HAS DESIGNATED UNICOM/CTAF FREQS IN THE 0.05 AND .25 MHZ INTERVALS TO RELIEVE THE CONGESTION ON THE LIMITED FREQS (122.7, 122.8, 122.9 AND 123.0 MHZ) ASSIGNED TO UNCTLED ARPTS AROUND THE COUNTRY. THE EQUIP IS IN PLACE. IT IS TIME TO SPLIT UP THE FREQS TO AVOID CONGESTION ON THE FREQ FOR OBVIOUS SAFETY REASONS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

A landing C172 is overtaken and almost hit on short final by another C172. Instructor pilot reporter cites the frequency overlap from nearby airports as blocking radio xmissions of aircraft in the traffic pattern.