Narrative:

Another example of similar callsign confusion caused by the use of four-digit call-signs. We had landed on runway 36L and were waiting for clearance to cross 36R. We heard; 'company thirty-five thirt???; without delay; cross 36R; contact ground'. We were not sure whether the transmission was meant for us or for company 3532 which had been on approach behind us and might have just landed. The controller began issuing instructions to other aircraft before we read back/clarified our clearance. We tried to confirm the call sign but only blocked tower's transmissions (including another; I believe; for us to cross). We continued to hold short until we could get a clear instruction from tower. Eventually; he told us to hold short for the landing traffic which turned out to be company 3532. The use of four-digit fleet call signs leads to very little phonetic difference between call signs. When read; the distinction between 3513 and 3532 is only expressed in the last of five syllables; and both of those distinguishing phonemes contain a 'T' sound ('-teen' and '-two'). Had we been using three-digit call signs and speaking each numeral separately; there would have been no confusion between 5-1-3 and 5-3-2. The solution is obvious: 1. End the use four-digit fleet call signs that are spoken as two numbers (e.g. 'Thirty-five-thir-teen') using a fourth digit does not add clarity when it causes the call sign to be spoken in exactly the same manner as several other flights. For example; a call sign beginning with 'thirty-five' cannot be differentiated from all of the other 'thirty-five' series call signs except by what follows. Company moreover; the following two digits which are also spoken as a number make the problem even worse. Someone in this company (or FAA) thinks that company 3513 and company flight 3532 are different call signs; but on the radio they sound very similar. It is much better to say five-one-three and five-three-two. 2. As a side note; the FAA's recent insistence of including the word 'flight' is also problematic because it is just another phoneme that is common to all call signs. The more that is common and the less that is distinctive; the more likely that transmissions will be missed; taken in error; or confused. 3. Company operations must have more common sense about assigning similar call signs. I understand that the permutations of call signs is limited; but they can be assigned in a way that does not lead to problems. Bcad and bcde can both be used; but they should not be next to each other in the arrival sequence. Using them at two separate times would have avoided a problem. So would assigning one to a flight that was arriving from the east.

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Original NASA ASRS Text

Title: Air carrier described confused runway crossing event listing the use of similar four digit call signs as the primary causal factor.

Narrative: Another example of SIMILAR CALLSIGN CONFUSION caused by the use of four-digit call-signs. We had landed on Runway 36L and were waiting for clearance to cross 36R. We heard; 'Company thirty-five thirt???; without delay; cross 36R; contact Ground'. We were not sure whether the transmission was meant for us or for Company 3532 which had been on approach behind us and might have just landed. The Controller began issuing instructions to other aircraft before we read back/clarified our clearance. We tried to confirm the call sign but only blocked Tower's transmissions (including another; I believe; for us to cross). We continued to hold short until we could get a clear instruction from Tower. Eventually; he told us to hold short for the landing traffic which turned out to be Company 3532. The use of four-digit fleet call signs leads to very little phonetic difference between call signs. When read; the distinction between 3513 and 3532 is only expressed in the last of five syllables; and both of those distinguishing phonemes contain a 'T' sound ('-teen' and '-two'). Had we been using three-digit call signs and speaking each numeral separately; there would have been no confusion between 5-1-3 and 5-3-2. The solution is obvious: 1. End the use four-digit fleet call signs that are spoken as two numbers (e.g. 'Thirty-five-thir-teen') Using a fourth digit does not add clarity when it causes the call sign to be spoken in exactly the same manner as several other flights. For example; a call sign beginning with 'thirty-five' cannot be differentiated from all of the other 'thirty-five' series call signs except by what follows. Company Moreover; the following two digits which are also spoken as a number make the problem even worse. Someone in this company (or FAA) thinks that Company 3513 and Company Flight 3532 are different call signs; but on the radio they sound very similar. It is much better to say FIVE-ONE-THREE and FIVE-THREE-TWO. 2. As a side note; the FAA's recent insistence of including the word 'flight' is also problematic because it is just another phoneme that is common to all call signs. The more that is common and the less that is distinctive; the more likely that transmissions will be missed; taken in error; or confused. 3. Company operations must have more common sense about assigning similar call signs. I understand that the permutations of call signs is limited; but they can be assigned in a way that does not lead to problems. BCAD and BCDE can both be used; but they should not be next to each other in the arrival sequence. Using them at two separate times would have avoided a problem. So would assigning one to a flight that was arriving from the East.

Data retrieved from NASA's ASRS site as of April 2012 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.