Origin of the 250 knots below 10,000 ft rule
Join Date: Dec 2000
Location: Canada
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First of all the rules in Canada and the USA specifically recognize the issue of safe operating speed requirements for some aircraft and allow operations in excess of 250 knots below 10,000 feet, so this is not an issue in North America. Controllers should be aware of this and are required to permit it.
I am intimately familiar with the strike data and bird flight patterns and agree that some limited numbers of birds do fly at the higher altitudes above 10,000 feet. However, there is very clear strike data and bird movement data to show that the likelihood of bird encounters decreases with altitude and that there is significant danger of encountering large and/or large flocking birds below 10,000 feet, but limited chance of encounter above 10,000 feet.
As for operating at high speed at 4 - 5,000 feet the data speaks for itself. The likelihood of an encounter with birds is significant and the impact force will in the majoority of cases exceed the certified impact force - the consequences are then not predictable, but again the strike reports speak for themselves, the probability of damage is high and the severity of the damage is far higher.
The major issue for consideration is how do we mitigate the risk? We can't see the birds easily and in fact many strikes occur at night and/or between cloud layers. There is no technology to track birds or predict their flight patterns on the aircraft, so if we can't see the hazard then we need to use other means to mitigate the risk. These are limited: keep the speed as low as safely possible, and spend the least amount of time in the bird rich altitudes.
The above statements are not meant to call into question the airmanship of pilots, but rather to educate pilots on the significant safety risk that high speed operations below 10,000 feet can present. The bird strike issue is not well understood by the majority of pilots and like past issues such as windshear, many pilots are operating with limited knowledge and making what they believe are good decisions - not macho decisions - just decisions that would benefit from more knowledge.
I am intimately familiar with the strike data and bird flight patterns and agree that some limited numbers of birds do fly at the higher altitudes above 10,000 feet. However, there is very clear strike data and bird movement data to show that the likelihood of bird encounters decreases with altitude and that there is significant danger of encountering large and/or large flocking birds below 10,000 feet, but limited chance of encounter above 10,000 feet.
As for operating at high speed at 4 - 5,000 feet the data speaks for itself. The likelihood of an encounter with birds is significant and the impact force will in the majoority of cases exceed the certified impact force - the consequences are then not predictable, but again the strike reports speak for themselves, the probability of damage is high and the severity of the damage is far higher.
The major issue for consideration is how do we mitigate the risk? We can't see the birds easily and in fact many strikes occur at night and/or between cloud layers. There is no technology to track birds or predict their flight patterns on the aircraft, so if we can't see the hazard then we need to use other means to mitigate the risk. These are limited: keep the speed as low as safely possible, and spend the least amount of time in the bird rich altitudes.
The above statements are not meant to call into question the airmanship of pilots, but rather to educate pilots on the significant safety risk that high speed operations below 10,000 feet can present. The bird strike issue is not well understood by the majority of pilots and like past issues such as windshear, many pilots are operating with limited knowledge and making what they believe are good decisions - not macho decisions - just decisions that would benefit from more knowledge.
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From all of the above it seems that there is a good case for an Aeronautical Information Circular warning pilots of the increased damage risk if a birdstrike was to occur when electing to use high speed below 10,000 ft. I don't think that Hudson was criticising operational reasons for high speed when he used the term macho. I have personally seen pilots trying to beat the competition by speeding up to 320K plus. That is macho...
Join Date: Apr 2001
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High speed below 10000 ft
I seem to recall a study carried out some years ago regarding high speed below 10000 ft, specifically, maintaining 320 kts until such time as it was necessary to slow to 180 kts for loc. intercept. According to this study, using LHR as the example, total time saved averaged 57 seconds.
I seem to recall a study carried out some years ago regarding high speed below 10000 ft, specifically, maintaining 320 kts until such time as it was necessary to slow to 180 kts for loc. intercept. According to this study, using LHR as the example, total time saved averaged 57 seconds.
