Origin of the 250 knots below 10,000 ft rule

[Hudson]

The 250 knot max speed below 10,000 ft has been around for a long time. From where did this rule originate? And what started it?

Is it because of collision risk (birds or other aircraft) minimisation? Or is it to standardise speeds below 10,000 ft purely for ATC purposes.

In Australian airspace, it is common practice for pilots of jets to request "high speed " climb below 10,000 ft - meaning they are happy to ignore the 250 knot tradition. It is just as common for ATC to request inbound aircraft to "cancel restriction" below 10,000 ft in order to facilitate flow control, and usually crews are happy to oblige.

While ATC might find it aids their task by encouraging high speed below 10,000 ft, it begs the question that if ICAO specified 250 knots below 10,000 ft for safety reasons, then why should this rule be broken so frequently in Australia by mutual agreement between pilots and ATC? Complacency on the part of both parties, perhaps?

[Groundloop]

I have always believed it came about after a mid-air collision over New York just after the first jets entered service.

16 December 1960. A United DC-8 was inbound to JFK (then known as Idlewild) from LAX. A TWA Super Connie was inbound to La Guardia from Columbus. The DC-8 began descent rather late and hence came down fast. Also it only had one VOR operational ( long before glass cockpits and sophisticated nav systems). While trying to get two radials from a single VOR the DC-8 crew overshoot their waypoint at nearly 400kts and collided with the Super Connie over Brooklyn. 128 + 6 on ground killed. After that the US introduced two requirements: speed limit of 250Kts below 10,000 feet and all large airliners must also be equiped with DME as well as VOR.

But I could be wrong!

[av8boy]

Timing seems right...

By May, 1961, only five months after the mid-air, the FAA was in the process of changing some aspects of Part 60 (Air Traffic Rules) of the Civil Air Regulations. One change had to do with amending the "Coded Radar Beacon Transponder Requirement in Positive Air Traffic Control Areas and Jet Advisory Areas," and another related to "Regulation of Aircraft Speed."

You may be interested to note that the FAA proposal (and subsequent rule) was for arriving traffic below 14,500, rather than 10,000. As proposed:
60.27 Aircraft Speed. Below 14,500 feet mean sea level and within 50 nautical miles of the airport of destination, no person shall operate an arriving aircraft at an indicated air speed in excess of 250 knots (288 mph) unless the operating limitations or military normal operating procedures require a greater minimum air speed, in which case the aircraft shall not be flown in excess of such speed.
There was a lot of comment on the proposed rule, including data arguing that it would cost airlines as much as $15,000,000 per year to comply.

The final rule adopted some of the arguments raised in the public comment period, and read as follows:
60.27 Aircraft speed.
A person shall not operate an arriving aircraft at an indicated airspeed in excess of 250 knots (288 m.p.h.) during flight below 10,000 feet mean sea level within 30 nautical miles of an airport where a landing is intended or where a simulated approach will be conducted unless the operating limitations or military normal operating procedures require a greater airspeed, in which case the aircraft shall not be flown in excess of such speed.

This amendment shall become effective on December 19, 1961.

(Sec. 307 of the Federal Aviation Act of 1958; 72 Stat. 749; 49 U.S.C. 1348)
Issued in Washington, D.C., on November 13, 1961.


Note that Part 60 did not address speed below 10,000 prior to this date, and, as I said, even with this change the limit only applied to arriving aircraft.

Interestingly, some commentors on the proposed rule argued that it would make ATC more difficult rather than easier...

I'd be happy to provide the full text of (what would now be called ) the Notice of Proposed Rulemaking as well as the announcement which went along with the new rule itself to anyone who would like to see it.

Dave

Edited to make note of the fact that in the 1960 mid-air, a minute before the collision United was out of 6,000 in the descent at 356 knots indicated...

[Spitoon]

I don't know what the origin was but most applications of the 250kt speed limit appear to be in airspace within which VFR flights might be operating (presumably to give them a fighting chance to see and avoid).

In the UK the limit only applies in certain airspaces/situations - which would seem to support this theory.

Returning to the orginal post, the 'no ATC speed restriction' may well be deresticting a procedural speed limit that is specified as, say, part of a SID or STAR. Certainly in the UK, individual controllers do not have the authority to permit aircraft to break the law.

[lomapaseo]

Certainly in the UK, individual controllers do not have the authority to permit aircraft to break the law.

My understanding is:

In the US it's considered a rule, as administered by the FAA administrator and not a law.

That way the FAA can administer relaxation etc., with due notice and public comment any time it pleases.

[411A]

Many years ago while flying out of BKK, used to accelerate to nearly the barber pole, as departing aircraft were restricted to 6000msl for quite some distance, at that time.

Then I hit a bird at 350 knots.
Just a little fellow, but it sure made a mess, just in front of my nose, on the windscreen.

A bigger bird would have been very bad news.
250 knots below 10,000 from then on.:ooh:

[Hudson]

What often happens in Australia is that when ATC "offer" no speed restriction below 10,000 on descent, some macho fliers accept this as some sort of challenge to their flying skills and play games on how late they can leave it at high speed (320 knots plus) before pulling the speed brakes and getting configured for final. The flight safety origin of the 250 knots "rule" is simply laughed off as wimpy.

But thank you so far for the excellent replies on the history behind the 250 knots restriction - it puts things in perspective.

[Lucky Angel]

I personally don't think that doing 320 kts will get you in a lot quicker. First of all it means descending earlier so you can make a level descelleration. This means reducing your TAS and increasing your fuel burn.I prefer to be 250kts by 10k.
The only time i might consider high speed below 10k is on the climb if given a low level off.

[whatunion]

youve obviously never tried 320 to 8 miles then!

[411A]

Those who insist that descending at high speed below 10,000 is a good idea, should have a rethink about the possible problems involved.
A really big bird for example.
In 1986, was doing a turnaround at Khartoum in a TriStar, and noticed a B727 at the edge of the ramp, the radome missing.
The local engineer told me that they had a really nasty encounter with a buzzard...the winged kind, not the chief pilot type:rolleyes:

At 340 KIAS, at 4000agl, the buzzard contacted the radome.
Thru it went...and thru the forward pressure bulkhead, broke the First Officers left leg, went thru the cockpit door (closed at the time), and ended up splattered all over the first class lounge.

Not a pretty sight.:ooh:

[lomapaseo]

411A

That would have been Ethiopian Airlines about a year prior to the B737 they lost due to birds.

The Sr VP wasn't very happy about his bad luck and jawed at me some about what could be done.

Unfortunately the airplane big bird rule is still 4 lbs, not 8 lbs even though they have insisted that engines now take 8 lb birds

[411A]

Indeed it was Ethiopian, Lomapaseo, and I have personally never seen such a mess anywhere else.
Blood, guts, and feathers all over.
Not to mention the new ventilation arrangements for the nose section.:\ :ooh:

Sure do hope the macho types that like high speed at low altitudes never find one of our big feathered friends in the process.

[ZFT]

411A

SAA had a very similar experience on a 732 about 15+ years ago. On that occasion elements of the P1 panel and the gore of the bird ended up in the Capts lap!!! (Again if I recall correctly, the Capt was Klaus Bonow)

[YMML]

I've wondered about this myself. The Jepps state that IFR aircraft in Class C airspace have no speed limit.. except SY, BN, ML, GC. I don't fly STAR's or SID's but believe the limit applies to them. To me the speed limit is the exception rather than the rule. Anyone have any other reference than Jepp- ATC- AU 511?

In any case Im limited by the AFM to 250kts below A080 for bird strike and agree with the previous words of caution...

[Hudson]

Back in the days when I flew real aeroplanes (four Rolls Royce Merlins), a Lincoln bomber was doing a supply drop on Willis Island, a remote atoll about 300 miles into the Coral Sea.

At 300 feet and 140 knots it clobbered a seagull which smashed through the left seat window taking out a fair portion of the pilots eye (he had a spare one on the other side of his nose, and being an NCO and not an officer it didn't matter that much!). The remains of the bird somehow funnelled down the rest of the fuselage inside the aircraft and smashed into the beer gut of the radio operator who just happened to be sitting near the main spar with his flying overalls half unzipped. He was shocked but unhurt.

The captain (an officer) had known the dangers to life and limb from birds that infested Willis Island, and had generously talked the second pilot (NCO) into actually sitting in the captain's seat during the supply drop. Meanwhile the captain took the second pilot's seat which was a much lower level in the cockpit and when he saw the bird coming, carefully ducked down below the coaming. You see, that's what experience tells you.


After the captain and navigator then pulled the badly injured NCO pilot who was all of 19 years old, out of the left seat, they slapped a bandage over his eyes and told him to hold the eye in place until they landed.

To cap this all off, the captain (officer) now flying from the second pilot's seat and a breezy cockpit plus a bitching blood spattered signaller, sent out a Mayday call on arrival in the circuit area because he had never landed a Lincoln from the RH seat.

The NCO recovered and in later years became a Wing Commander winning the DFC and AFC even though he had a wonky eye. Better still, he also married the pretty nurse that took care of him in hospital.

I don't know what the morale of the story is except that even 250 below 10 grand has its drawbacks when it comes to bird-strike.

[Canuckbirdstrike]

To all:

I completed a risk analysis on high-speed flight below 10,000 feet for Transport Canada a couple of years ago. The analysis was commissioned out of concerns over the increasing large flocking bird population numbers in North America and the need to understand the safety risk vs. the economic benefits.

While researching the issues I obtained the following historical background on the 250 knots below 10,000 foot rule:

FAR 91.117 (a) states: Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 mph).

As reported in another post, the rule was established after a mid-air collision over Staten Island. However, there had also been two other mid-air collisions around that time period. The FAA originally considered implementing a rule restricting airspeed to 250 knots below 14,500 feet MSL but compromised at 10,000. In fact an early draft called for 160 knots at 14,500.

What is most fascinating is that from this point forward current airframe and engine rules were developed based on this regulatory speed requirement, using 250 kias as a test condition.

My research of the certification standards, the North American bird strike data and the potential efficiencies revealed that 60% of bird encounters above 3,000 feet AGL involved raptors or waterfowl. What is interesting is that as altitude increased the percentage increased. Waterfowl and raptors present a significant risk due to the fact that their mean weights exceed the engine and airframe certification standards for the majority of the current world fleet and for waterfowl these encounters will be with flocks – something that the certification standards do not contemplate. Couple this with the fact that of the birds in North America; 14 species with a mean weight above 8 lbs, 13 have an increasing population trend and for the 31 species with a mean weight between 4 and 8 lbs, 24 were increasing and 5 were stable, and we have significant increasing safety risk.

I then analyzed impact forces based on the FARs and compared the calculated impact force for various bird weights at different indicated airspeeds. The results are very sobering. Due to the fact that impact force increases as a function of the square of the TAS, a constant IAS climb leads to increasing impact forces. In fact if you hit a 4 lb bird at 300 KIAS at an altitude greater than 4,500 feet you will exceed the certified airframe strike impact force for many jet aircraft.

If one examines the potential system efficiencies of high speed operations below 10,000 feet there is no conclusive data to show that there are any meaningful increases in efficiency. The key here is to examine the total efficiency of the traffic system – if a number of aircraft are accelerated above 250 KIAS and ATC requires them to fly the same speed for traffic separation, a number of aircraft may gain slight efficiency advantages, but a number will also incur penalties. This can easily be seen by examining the range of ECON climb speeds that an FMS will generate if the speed limit is removed, they can vary from 265 – 315 KIAS on the narrow body airbus fleet (A319, A320, A321). The net result is that there is limited if any overall system efficiency increase.

When you consolidate all the above information; regulatory history, certification standards, bird strike data, bird species population data, impact forces and limited efficiency gains there is no reasonable safe case to allow high speed flight departures below 10,000 feet.

The preceding information is only an outline of the report. I will try and see if I can obtain from Transport Canada to post the entire report.

If any of you wish to read further information on bird strike issues please take the time to visit the Transport Canada website and download/read “Sharing the Skies” a compendium of bird strike information. It is an excellent resource and safety tool.

The URL is: http://www.tc.gc.ca/CivilAviation/Aerodrome/WildlifeControl/tp13549/menu.htm

Richard Sowden
A320 Captain and bird strike researcher

[lomapaseo]

Canuckbirdstrike

In your post above and I am sure your paper as well, makes an excellent point for discussion.

However you do need to better take into account the regulatory conditions of the past and today. For instance your quote

What is most fascinating is that from this point forward current airframe and engine rules were developed based on this regulatory speed requirement, using 250 kias as a test condition.


This is not entirely correct even though some of your concerns are still valid.

For instance the aircraft regulation considers § 25.631 Bird strike damage.
The empennage structure must be designed to assure capability of continued safe flight and landing of the airplane after impact with an 8-pound bird when the velocity of the airplane (relative to the bird along the airplane's flight path) is equal to V¯C¯ at sea level .....

What is not specifically addressed in this regulation are multiple birds affecting multiple systems.

Regarding the engines. The 250kts does not necessarily increase the loading on the spinning fan blades. When one considers the effective incidence angle on the large open faced fans so common in todays high-bypass-ratio engines, the loading is a parabolic curve function of aircraft speed. i.e. as the speed increases from zero the loading on the blade increases until it maxes out somewhere about 180 kts to 210 kts thereafter it falls off until a pass through condition exists at about 450-500 kts and above this the bird will actually impact on the front face of the blades.

Thus for the spinning blade the speed of the blade must be resolved as a vector with the speed of the bird's entrance. This is taken into account by requiring the engije ingestions tests to be designed around conditions of takeoff up to initial climb speeds (below 250kts)

This inments for concern, since the effect on static structures both within the propulsion system (inlet lips, nose spinners and behind the fan struts) as well as frontal surfaces of the aircraft are certainly going to be affected by statistically increasing the bird encounter speed to 250kts

[Canuckbirdstrike]

Lomapaseo:

Please excuse my poor communication of the issue of the regulatory impact of the change to 250 knots, I obviously did not get the message across that I wanted.

The message I was trying to communicate is that regulators involved with strike impact certfication were not as concerned with the issue of striking larger birds because they believed that one of the mitigations being used was to limit the IAS to 250 KIAS on climb. Not so in many jurisdictions.

I am fully aware of the FAR 25 requirements and indeed the FAR you quoted is only applicable to the empennage (as the result of a 1962 Viscount crash). The rest of the structure is only certified for a 4 lb bird. My analysis did take into account the use of Vc for the impact speed and the examples I cite were based on a Vc of 320 knots and a 4 lb bird.

Thanks for posting the explanation on blade loading and airspeed. I am well aware of this issue, but believe it is valuable for others to understand the concept. One very important issue is the fact that other than the ultra-large fan engines on the B777 that were voluntarily certified for an 8 lb bird, the current engines being used in the overwhelming majority of aircraft are only certified for a 4 lb bird. The weights of migratory waterfowl are well above this and high speed operations do present a high risk to engine structures.

One point I forgot to mention is the issue of the aircraft acceleration manever - from 250 knots to high speed climb. During this maneuver rate of climb typically is reduced by 50%. The aircraft is accelerating, climb rate is reduced and all this occurs at the bird rich altitudes. Therefore, the classic high risk is occurring - exposure, probability and severity are all increasing.

There have been enough recent incidents with geese where the aircraft structure has been damaged extensively, bordering on catatstrophic failure, that to increase the speed at low altitude is foolhardy.

[Mr.Buzzy]

There was also an incident near Broome in Western Australia involving a Dash 8 and a large bird, a 30cm crack to the main spar, loss of a hydraulic system, subsequent in flight shutdown...etc etc and the dash only does 242 kn!
250 below 10000 wouldnt have helped.
Managed risk I guess... we could play the "what if" game all day.

One thing I have noticed though is that When ATC ask for max speed on descent we are having a great day if Progress page 1 shows a one minute savings in time!

[Old Smokey]

A lot of valid discussion here regarding bird strike risk, originating from a convention (converted to a rule, but never a law) that aircraft be restricted to 250 KIAS below 10000 feet. Unfortunately, a great many birds exceed the statutory limit of 10000 feet, thus, if bird strike risk was a significant factor, we should lift the limiting altitude even higher. Like most of the posts here, I'm digressing from the intent of the original post, so let's put birds aside for the moment.

The origin of the rule, and indeed it's fairly recent application in Australia, stems from the desire to more effectively regulate traffic flow, and this it does. Fortunately, Australia is possessed of Air Traffic Controllers who recognise it as a convention, and apply a certain degree of flexibility in this, and a number of other conventions WHEN TRAFFIC FLOW PERMITS. The Aussie controllers, for example, frequently allow cruise at non-standard levels when traffic permits, and speed in excess of 250 KIAS below 10000 feet when traffic permits - Indeed it may improve traffic flow to have someone fly faster to increase the spacing with slower traffic behind.

For a great number of heavy aircraft, my own included, the aircraft flies like a brick at 250 KIAS with much reduced manoeuvre margins. I note that for my own aircraft, minimum manoeuvre speed at Max Weight is 248 KIAS, providing protection of a mere 1.2 G before stall, turbulence penetration speed of 280 KIAS provides 1.6 G protection, just enough to tolerate MODERATE turbulence. When I'm facing stormy turbulent conditions in Australian terminal areas, I advise of a REQUIREMENT to increase speed, not a request, it's a safety issue. Thank goodness for the flexible and practical Aussie controllers, and the Yanks at 'inflexible' LAX, and the allegedly 'VERY inflexible' Taiwanese controllers, etc. etc. I suppose that, in the terms of reference used by one of the contributors here, I'm a macho pilot - No Sir! I'll leave the macho stuff to the guys who want to go do stalling practice in thunderstorms with 350 to 400 passengers on board.

There's minimal commercial advantage in maintaining high speed below 10000 on descent, but to insinuate that 320 KIAS at ATC request down to 4 or 5000 feet is macho stuff is plain ridiculous and an insult to capabilities of the thousands of VERY conservative airmen who do it every day.

[Canuckbirdstrike]

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.

[Hudson]

Canuckbirdstrike. Thank you for the excellent background information. I have always been uneasy about the happy acceptance of high speed below 10 with people simply ignoring the very real dangers of impact damage.

[Menen]

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...

[Stickies]

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.