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Why are Oscar, India, and X-Ray (O, I, and X) not used as taxiway identifiers?

What are the curved centerlines at taxiway intersections for?Why is Denver International Airport runway 16R/34L rarely used?Why are offset lead-in arcs used?Why are most runways made of asphalt and not concrete?Are flexible pavements not recommended in hot climates?Why are many runways used just for departures/arrivals?What is the runway holding short line on Taxiway B between B2 and B3 at KFAT for RWY29L?Why all the taxiway construction at PHL?What is the area between the taxiway and runway shown in the picture below?

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34

2

$begingroup$

An old CAR "Licensing of Aerodromes" document indicated that taxiways may not be designated by O, I, or X.

Is this still in effect today? Why were (or are) those not used as taxiway identifiers?

My guess is that the shapes of those letters could cause confusion such as an "X" meaning something like "closed" or I looking like a vertical line "|".

airport-design airport-markings

share|improve this question

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

$endgroup$

• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  $begingroup$
  The 1990 Wayne County Airport runway collision happened because they missed the turn onto taxiway "Oscar 6", and again when instructed to turn onto XRay but instead turned onto Runway 03C. I believe DTW renamed the runways/taxiways after this (but not sure if one correlates the other) because there is no longer a taxiway "O6", "X" or a runway 03C.
  $endgroup$
  – Ron Beyer
  Jul 22 at 5:12
  

  
  
  
  


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  @RonBeyer that airport is known to most people as "Detroit Metro", DTW, or just "Detroit", where it would be perfectly normal for two jetliners to be. There is another major airport in Wayne County that is airline-capable, but it is GA only. When you don't use Metro/DTW by one of its proper names, people might think you mean the other...
  $endgroup$
  – Harper
  Jul 22 at 18:26
  
  

  
  
  
  


• 
  
  
  

  
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  @Harper That's the title of the Wikipedia article I linked to, which is why I used it. I personally refer to it as DTW (and did so in my post), so there shouldn't be any confusion about what airport I'm referring to.
  $endgroup$
  – Ron Beyer
  Jul 22 at 20:22
  

  
  
  
  


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  That page is amazingly sparse. I assume the 727 was able to successfully take off before returning, given the relatively small amount of damage for such an awful situation.
  $endgroup$
  – zymhan
  Jul 23 at 14:06
  

  
  
  
  


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  @zymhan: According to the accident report (PDF), the captain "rejected the takeoff and stopped the airplane using maximum braking."
  $endgroup$
  – Fred Larson
  Jul 23 at 18:51
  

  
  
  
  

 | 
show 1 more comment

34

2

$begingroup$

An old CAR "Licensing of Aerodromes" document indicated that taxiways may not be designated by O, I, or X.

Is this still in effect today? Why were (or are) those not used as taxiway identifiers?

My guess is that the shapes of those letters could cause confusion such as an "X" meaning something like "closed" or I looking like a vertical line "|".

airport-design airport-markings

share|improve this question

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

$endgroup$

• 
  
  
  

  
  11
  

  
  
  
  
  
  

  
  $begingroup$
  The 1990 Wayne County Airport runway collision happened because they missed the turn onto taxiway "Oscar 6", and again when instructed to turn onto XRay but instead turned onto Runway 03C. I believe DTW renamed the runways/taxiways after this (but not sure if one correlates the other) because there is no longer a taxiway "O6", "X" or a runway 03C.
  $endgroup$
  – Ron Beyer
  Jul 22 at 5:12
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  @RonBeyer that airport is known to most people as "Detroit Metro", DTW, or just "Detroit", where it would be perfectly normal for two jetliners to be. There is another major airport in Wayne County that is airline-capable, but it is GA only. When you don't use Metro/DTW by one of its proper names, people might think you mean the other...
  $endgroup$
  – Harper
  Jul 22 at 18:26
  
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  $begingroup$
  @Harper That's the title of the Wikipedia article I linked to, which is why I used it. I personally refer to it as DTW (and did so in my post), so there shouldn't be any confusion about what airport I'm referring to.
  $endgroup$
  – Ron Beyer
  Jul 22 at 20:22
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  That page is amazingly sparse. I assume the 727 was able to successfully take off before returning, given the relatively small amount of damage for such an awful situation.
  $endgroup$
  – zymhan
  Jul 23 at 14:06
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  $begingroup$
  @zymhan: According to the accident report (PDF), the captain "rejected the takeoff and stopped the airplane using maximum braking."
  $endgroup$
  – Fred Larson
  Jul 23 at 18:51
  

  
  
  
  

 | 
show 1 more comment

$begingroup$

An old CAR "Licensing of Aerodromes" document indicated that taxiways may not be designated by O, I, or X.

Is this still in effect today? Why were (or are) those not used as taxiway identifiers?

My guess is that the shapes of those letters could cause confusion such as an "X" meaning something like "closed" or I looking like a vertical line "|".

airport-design airport-markings

share|improve this question

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

$endgroup$

share|improve this question

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

share|improve this question

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

asked Jul 22 at 4:48

Ryan MortensenRyan Mortensen

4,4311515 silver badges4848 bronze badges

2 Answers
2

active

oldest

votes

70

$begingroup$

Because those symbols are easily confused with the number 0, the number 1 and the symbol for a closed runway/taxiway (✕) respectively.

(1) Numbers by themselves, and the letters "I" and "O" must not be used because they could be mistaken for a runway number.

(2) The letter "X" must not be used because a sign with an "X" could be misconstrued as indicating a closed taxiway or runway.

Source: FAA Engineering Brief No. 89 on Taxiway Nomenclature Convention (via SKYbrary.aero).

Most aerodromes do refrain from using these identifiers, but there are also examples of them being used. For example, Copenhagen (EKCH) has a taxiway I(ndia).

share|improve this answer

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Interesting. Nice catch
  $endgroup$
  – Carlo Felicione
  Jul 22 at 19:05
  

  
  
  
  


• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  $begingroup$
  So does ICAO, from Annex 14: 5.4.3.36 Recommendation.— When designating taxiways, the use of the letters I, O or X and the use of words such as inner and outer should be avoided wherever possible to avoid confusion with the numerals 1, 0 and closed marking.
  $endgroup$
  – ymb1
  Jul 22 at 19:07
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @ymb1 Thanks! Was looking for an ICAO reference, but stumbled upon the FAA document first :)
  $endgroup$
  – J. Hougaard
  Jul 23 at 6:14
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Something very similar happens in rehearsal letters in music: music.stackexchange.com/questions/86569/…
  $endgroup$
  – Maika Sakuranomiya
  Oct 22 at 1:55
  

  
  
  
  

add a comment
 | 

11

$begingroup$

"X" marks a closed runway or an airstrip where aircraft may not land. See this temporary marker as an example of how it is used.

I have tow-launched hang gliders from an old WWII airstrip in Suffolk (England), which was shared with microlight pilots. We had one of these markers which we laid out before flying, to prevent other aircraft from inadvertently landing there whilst we were towing.

share|improve this answer

edited Jul 23 at 10:21

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges

$endgroup$

add a comment
 | 

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70

$begingroup$

Because those symbols are easily confused with the number 0, the number 1 and the symbol for a closed runway/taxiway (✕) respectively.

(1) Numbers by themselves, and the letters "I" and "O" must not be used because they could be mistaken for a runway number.

(2) The letter "X" must not be used because a sign with an "X" could be misconstrued as indicating a closed taxiway or runway.

Source: FAA Engineering Brief No. 89 on Taxiway Nomenclature Convention (via SKYbrary.aero).

Most aerodromes do refrain from using these identifiers, but there are also examples of them being used. For example, Copenhagen (EKCH) has a taxiway I(ndia).

share|improve this answer

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Interesting. Nice catch
  $endgroup$
  – Carlo Felicione
  Jul 22 at 19:05
  

  
  
  
  


• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  $begingroup$
  So does ICAO, from Annex 14: 5.4.3.36 Recommendation.— When designating taxiways, the use of the letters I, O or X and the use of words such as inner and outer should be avoided wherever possible to avoid confusion with the numerals 1, 0 and closed marking.
  $endgroup$
  – ymb1
  Jul 22 at 19:07
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @ymb1 Thanks! Was looking for an ICAO reference, but stumbled upon the FAA document first :)
  $endgroup$
  – J. Hougaard
  Jul 23 at 6:14
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Something very similar happens in rehearsal letters in music: music.stackexchange.com/questions/86569/…
  $endgroup$
  – Maika Sakuranomiya
  Oct 22 at 1:55
  

  
  
  
  

add a comment
 | 

70

$begingroup$

Because those symbols are easily confused with the number 0, the number 1 and the symbol for a closed runway/taxiway (✕) respectively.

(1) Numbers by themselves, and the letters "I" and "O" must not be used because they could be mistaken for a runway number.

(2) The letter "X" must not be used because a sign with an "X" could be misconstrued as indicating a closed taxiway or runway.

Source: FAA Engineering Brief No. 89 on Taxiway Nomenclature Convention (via SKYbrary.aero).

Most aerodromes do refrain from using these identifiers, but there are also examples of them being used. For example, Copenhagen (EKCH) has a taxiway I(ndia).

share|improve this answer

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Interesting. Nice catch
  $endgroup$
  – Carlo Felicione
  Jul 22 at 19:05
  

  
  
  
  


• 
  
  
  

  
  8
  

  
  
  
  
  
  

  
  $begingroup$
  So does ICAO, from Annex 14: 5.4.3.36 Recommendation.— When designating taxiways, the use of the letters I, O or X and the use of words such as inner and outer should be avoided wherever possible to avoid confusion with the numerals 1, 0 and closed marking.
  $endgroup$
  – ymb1
  Jul 22 at 19:07
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  @ymb1 Thanks! Was looking for an ICAO reference, but stumbled upon the FAA document first :)
  $endgroup$
  – J. Hougaard
  Jul 23 at 6:14
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Something very similar happens in rehearsal letters in music: music.stackexchange.com/questions/86569/…
  $endgroup$
  – Maika Sakuranomiya
  Oct 22 at 1:55
  

  
  
  
  

add a comment
 | 

$begingroup$

Because those symbols are easily confused with the number 0, the number 1 and the symbol for a closed runway/taxiway (✕) respectively.

(1) Numbers by themselves, and the letters "I" and "O" must not be used because they could be mistaken for a runway number.

(2) The letter "X" must not be used because a sign with an "X" could be misconstrued as indicating a closed taxiway or runway.

Source: FAA Engineering Brief No. 89 on Taxiway Nomenclature Convention (via SKYbrary.aero).

Most aerodromes do refrain from using these identifiers, but there are also examples of them being used. For example, Copenhagen (EKCH) has a taxiway I(ndia).

share|improve this answer

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

$endgroup$

share|improve this answer

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

edited Jul 22 at 18:57

ymb1

82.2k99 gold badges271271 silver badges450450 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

answered Jul 22 at 5:54

J. HougaardJ. Hougaard

21.5k22 gold badges8484 silver badges113113 bronze badges

11

$begingroup$

"X" marks a closed runway or an airstrip where aircraft may not land. See this temporary marker as an example of how it is used.

I have tow-launched hang gliders from an old WWII airstrip in Suffolk (England), which was shared with microlight pilots. We had one of these markers which we laid out before flying, to prevent other aircraft from inadvertently landing there whilst we were towing.

share|improve this answer

edited Jul 23 at 10:21

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges

$endgroup$

add a comment
 | 

11

$begingroup$

"X" marks a closed runway or an airstrip where aircraft may not land. See this temporary marker as an example of how it is used.

I have tow-launched hang gliders from an old WWII airstrip in Suffolk (England), which was shared with microlight pilots. We had one of these markers which we laid out before flying, to prevent other aircraft from inadvertently landing there whilst we were towing.

share|improve this answer

edited Jul 23 at 10:21

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges

$endgroup$

add a comment
 | 

$begingroup$

"X" marks a closed runway or an airstrip where aircraft may not land. See this temporary marker as an example of how it is used.

I have tow-launched hang gliders from an old WWII airstrip in Suffolk (England), which was shared with microlight pilots. We had one of these markers which we laid out before flying, to prevent other aircraft from inadvertently landing there whilst we were towing.

share|improve this answer

edited Jul 23 at 10:21

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges

$endgroup$

share|improve this answer

edited Jul 23 at 10:21

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges

answered Jul 23 at 10:09

GrahamGraham

1,57166 silver badges1111 bronze badges