U.S. Department

of Transportation


Federal Aviation



Air Traffic


A Communication from the  

Vice President,
  System Operations Services


Issue # 2004-6

October 2004                                                                                             

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In this Issue:
Abbreviated Transmissions
Weather Product Classification
Issuance of Safety Alerts

Abbreviated Transmissions
A fatal aircraft crash occurred in mountainous terrain shortly after completion of a radar handoff and communications transfer from an en route to a terminal facility.  At the time there were three aircraft with similar call signs on the terminal controller's frequency.  The accident aircraft took a descent clearance intended for one of the other aircraft with a similar sounding call sign.  The controller used an abbreviated call sign when issuing the descent clearance and did not catch the incorrect readback.

Federal Aviation Administration Order (FAAO) 7110.65, paragraph 2-4-9, states: "Use the identification prefix and the last 3 digits or letters of the aircraft identification after communications have been established.  Do not abbreviate similar sounding aircraft identifications or the identification of an air carrier or other civil aircraft having an FAA authorized call sign."  Additionally, paragraph 2‑4‑20 states that you shall, "Use the full identification in reply to aircraft with similar sounding identifications."  In this incident, the company had filed the three similar call signs. 

Further guidance is contained in paragraph 2-4-15, which states: "Emphasize appropriate digits, letters, or similar sounding words to aid in distinguishing between similar sounding aircraft identifications.  Additionally:

 a.  Notify each pilot concerned when communicating with aircraft having similar sounding identifications.


'United Thirty-one United, Miami Center, U.S.  Air Thirty-one is also on this frequency, acknowledge.'

'U.S.  Air Thirty-one U.S.  Air, Miami Center, United Thirty-one is also on this frequency, acknowledge.'

 b.  Notify the operations supervisor-in-charge of any duplicate flight identification numbers or phonetically similar-sounding call signs when the aircraft are operating simultaneously within the same sector."

As much as the companies try not to schedule similar sounding call signs arriving at the same airport at the same time, eventually there will be the occurrence of similar call signs at hub facilities.  There is also the possibility of similar sounding call signs at any airport, as evidenced by this accident that occurred while the three aircraft were on approach to an airport that serves primarily general aviation, with commuter airline service. 

FAAO 7210.3, paragraph 2-1-12, states in part:  "To alleviate any potential misunderstandings of aircraft identifications caused by duplicate, phonetically similar-sounding, or hard to distinguish registration numbers or call signs operating in the same area, facility managers shall ensure that operations supervisors report those occurrences to a facility officer."  Appropriate action should be taken as outlined in paragraph 2-1-12.  For example, for civil aircraft other than air carrier, advise the Office of Terminal Safety and Operations Support or the Office of En Route Safety and Operations Support when two or more designated call signs are found to be phonetically similar or difficult to pronounce and are causing a flight identification problem.

In summary, emphasize the appropriate digits, letters, or similar sounding words to aid in distinguishing between the aircraft.  Additionally, notify each pilot of the other to advise they are both on the same frequency.  Also, provide the information to the supervisor so the appropriate actions outlined in FAAO 7210.3 can be taken.  (ATO-T)

Weather Product Classification

/*F/TER Over the last 12 years, the FAA developed and funded a substantial aviation weather research and development program to create new aviation weather products.  The development of these new weather products is an evolutionary process with distinct stages of maturity and often the products are accessible via the public Internet for test and evaluation purposes prior to their being ready for use in aviation operations.  In addition, some of the new aviation weather products are designed for specific users such as meteorologists and dispatchers.  This caused confusion within the aviation community regarding the relationship between regulatory requirements and new weather products.  To clarify the proper use of aviation weather products to meet regulatory requirements, the FAA developed definitions of primary and supplementary weather products.

Primary products are those aviation weather products that meet all the regulatory requirements and safety needs for use in making flight-related aviation weather decisions.  Supplementary products may be used for enhanced situational awareness but not to meet aviation weather regulatory requirements.  Supplementary products must be used in conjunction with one or more primary weather products.

The FAA may further restrict the use of supplementary weather products through limitations described in the product label.   An aviation weather product produced by the Federal Government or an entity with which it has a contractual relationship is a primary product unless designated as a supplementary product by the FAA.

Some examples of primary products are significant meteorological information (SIGMET), convective SIGMETs, airmen's meteorological information (AIRMET), and aviation routine weather reports (METAR).  Supplementary weather products are generally newly developed aviation weather products available via the aviation digital data service (ADDS) website.  At this time, only a few supplementary products exist including current icing potential (CIP), forecasting icing potential (FIP), and national convective weather forecast (NCWF).

The August 2004 edition of the Aeronautical Information Manual (AIM) introduces the weather product definitions to the general aviation community.  As automated flight service station controllers, you may receive questions from pilots regarding this new classification of aviation weather products.  (ATO-D)

Issuance of Safety Alerts

/*ET/ A fatal aircraft crash occurred in mountainous terrain shortly after completion of a radar handoff and communications transfer from an en route to a terminal facility.  The aircraft took a descent clearance issued by the terminal controller intended for another aircraft with a similar call sign.  The terminal controller did not catch the incorrect readback or observe the aircraft's descent.

The aircraft was operating at the minimum instrument flight rules altitude at the time of the transfer so the en route controller received an en route minimum safe altitude warning (E-MSAW) when the aircraft began its descent.  The en route controller suppressed the E-MSAW alert after approximately one minute and subsequently suppressed display of the data block but did not contact or alert the terminal controller.

FAAO 7110.65, Air Traffic Control, Para-graph 2‑1‑6, Safety Alert, states in part:  "Issue a safety alert to an aircraft if you are aware the aircraft is in a position/altitude which, in your judgment, places it in unsafe proximity to terrain, obstructions, or other aircraft.  Once the pilot informs you action is being taken to resolve the situation, you may discontinue the issuance of further alerts.  Do not assume that because someone else has responsibility for the aircraft that the unsafe situation has been observed and the safety alert issued; inform the appropriate controller."

Paragraph 5-14-2, En Route Minimum Safe Altitude Warning (E-MSAW), subparagraph a,  states: "When an E-MSAW alert is displayed, immediately analyze the situation and, if necessary, take the appropriate action to resolve the alert."

Subparagraph c  states: "The computer entry of a message suppressing or inhibiting E-MSAW alerts constitutes acknowledgement for the alert and indicates that appropriate action has or will be taken to resolve the situation."

Based on the information available, had the en route controller correctly applied the above referenced paragraphs, the terminal controller would have been notified of the E-MSAW alert and the pilot may not have died.  (ATO-E)