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Increasing Range of Speeds for Same Aircraft Type/Response
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The entries below include the responses forwarded through APAA and a general ERAA response. The eight operator responses collected by ERAA using a survey format are available separately on the bookshelf - to view them, click here.
- We experience the highlighted issue as well. In our experience, the problem not only extends to forward speeds, but also to vertical speeds. Our controllers rely greatly on these to achieve separation and we have indications that it is becoming harder to rely on expected rates and speeds. What is more, we have the impression that some pilots are having problems as well anticipating what their aircraft will and will not do, especially with regards to climb profiles. Quite often, they would commit to a minimum rate or a clearance limit, only to just not make it. In that sense, it would be highly desirable to impose a minimum vertical rate for both climbs and descends. If the vertical rate would drop below, the pilot should advise ATC. It is very hard for controllers to adapt to changes such as this, as there appears to be a certain randomness about them - a company may override their normal profiles, depending on situations which are not known to the controllers. It is very hard to train for this randomness: in our simulator, a BOEING 737-400 is a B734, whether it is company X or company Y. A large part of OJTI is finding these patterns and taking them into account. When they change or become unpredictable, the job becomes a lot harder (workload increase). Having said that, the safety implications are usually rather limited, with marginal horizontal or vertical separation infringements.
- BOEING 747-400 (international, winglets) - We have always used cruise mach into 300kts for descent profiles but with increasing fuel costs an Econ descent offers significant fuel savings. This however would have our indicated descent speeds on the 744 varying from 340 kts629.68 km/h <br />174.76 m/s <br /> to 250kts depending mainly on weight and can see why issues are developing if operators are randomly applying. B747 - There have, for 20 years plus, been differences in 747 climb and cruise speeds based on aircraft weight and/or Cost Indexes. In climb this could make 50 kts92.6 km/h <br />25.7 m/s <br /> difference. In CRZ the same. Even on approach the difference in speed between a lightly loaded 747 a heavy one can be over 30 kts. Operating this way was has never been a problem - anywhere. It worries me that ATC claim that this is a new phenomena. The same logic for fuel savings also applies to descent planning, we should be adjusting our descent speeds and planning to save fuel, but the majority of airlines do not adjust the descent speed. It is just not practical at most major airports due to ATC imposed limitations. There may be non- radar environments, airports or FIRs where specific issues have surfaced recently but differences in climb speeds for the same aircraft type have been a feature of widebody jet operations for decades. With regard to advising ATC of changes to speed of greater than 5% - this does not happen in practice. At FL 260, a heavy weight 747 at LRC should CRZ at Mach .845/ IAS 352 kts. A light 747 at the same level should be CRZing at Mach .715/ IAS 295 kts546.34 km/h <br />151.63 m/s <br />. ATC are not advised if we are held down at lower levels - even though this may make a significant difference to speeds. This is not a safety issue, it is an ATC work practices issue. B777 Series - I think they are right. The Speed Disparity will become the norm. ECON descent speeds very much depend on aircraft type and, within each type, the aircraft weight. Traditionally, busy airports place 'speed controls' towards the end of descent, typically below 10,000 and in the approach sequence. It may be that ATC now need to consider their options during the early part of the descent as well. Is it a safety issue? I don't think so. Just needs awareness from ATC and direction / restriction where necessary.
- We have shifted to variable cost index operation to allow our pilots the flexibility to reduce their cost index, and therefore airspeed, whenever their estimated time of arrival at destination is earlier than published or whenever heavy traffic is expected at TMA. The practice saves a significant amount of fuel. But the pilot needs to advise ATC his new airspeed or mach no. and revised estimate of next reporting points. The earlier the change is made, the more fuel is saved. In cases where there is traffic in the vicinity, ATC normally issues a speed for the aircraft to maintain. If at all possible, perhaps a required time over a particular waypoint may be more in keeping with the practice of variable cost index. What is certain is we need to find a solution to allow operators to save fuel and reduce carbon emissions, while operating in a safe environment.
- Traffic conditions permitting, ATC should always allow FMS Cost Index designated climb/descent speeds for operational efficiency, fuel savings and environment protection (less CO2 and NOx with less fuel burnt). For required traffic sequencing which ATC is unable to accept variable climb/descent speeds, most airlines will cooperate with given speed assignments, even though we prefer to seek our own optimum speeds to fly base on aircraft type, aircraft weight and the environment.
- (We are) concerned about fuel efficiency very much. We are reviewing our operation to reduce fuel cost now but we would like to explain our current operation. We set the fixed Cost Index depending upon the aircraft type as normal speed and most pilots fly at the Cost Index as long as the specific speed is not required by ATC or company. We determine the Cost Index considering the manufacture’s design cruise speed, change of fuel and time by Cost Index and speed at climb and descent phase, etc. For example, CI [100LB/hour] = 100 for B747, 80 for B777 and 40 for AIRBUS A-320. The merit of Cost Index is that we can manage the speed through all flight phase and the speed is considering appropriate margin to buffet and VMO/MMO. As mentioned in this paper, the climb and descent speed varies very much by airlines, aircraft type and flight range. For descent, FMC calculates the top of descent point based on the descent speed schedule and it is most efficient to start descent at the point. If ATC specifies the speed during descent, the flight path deviates from ideal path and aircraft consumes additional fuel. If ATC requires speed control to manage the traffic, we prefer to notice the speed before descent to recalculate the top of descent point based on the specified speed. We think the goal of this concept is CDA (Continuous Descent Arrival). Descend speed advised by ATC for minimizing track distance before descent is much appreciated. On the other hand, concerning about climb speed, it is difficult to fly the certain common speed because climb speed is rather depending on aircraft type and weight. Especially for long range flight, we require the higher climb speed to keep the maneuvering margin to stall speed. For example, the climb speed of B777-300ER is 320 KCAS. And we think it is important to control climb profile besides of climb speed for ATC but it is difficult to control climb rate. We think it is no mean to specify the climb speed as mentioned above and it is not preferable by safety reason that is adequate maneuvering margin. For radar vectoring aircrafts, compare with controlling approaching/landing traffics, controlling departing traffics is easy to keep separation because of enough airspace for diverging tracks.
- I try my best to describe what we are doing. It is more or less the same for all fleets, so I chose a A320 to explain. First reason for the unpredictable speeds: Usually we get a flight plan filed with so called "ECON SPEEDS". These are calculated with a low cost index giving the usual climb speeds around 300 kts555.6 km/h <br />154.2 m/s <br />. The transition from IAS to MACH takes place automatically when passing the appropriate MACH NO in climb and passing the IAS in descent. On an ECON profile the climb and cruise MACH will be around .77 or .78. The descent speed around 280 kts, sometimes even lower. Now, during some time in the climb, after we got the first estimated time of arrival from the FMS, we decide which Cost Index (CI), we actually want to fly. Since ground times are getting shorter and due to increasing traffic, holding patterns are getting more probable, we are usually on the late side. In this case, we switch from a low CI to a high one, giving us speeds of 340kts/M.80 for all flight phases above FL100 (max speeds for our aircraft type). We do this without informing ATC - not saying that this is good, it just has become practice... In very, very rare cases, when we are expecting an arrival time before the planned time, we can reduce the CI even further, giving us speeds around 280/M.74. Second reason for unpredictable speeds: Especially during climb speed changes can occur when passing clouds. Since the flight attendants should not start the service while still in turbulent air, we try to get above the clouds as quickly as possible using a low climb speed (as low as 220 or 250 kts463 km/h <br />128.5 m/s <br /> IAS up the FLs as high as 300, to give a range). Once above the clouds, we may change directly from 220kts to 340kts indicated, to catch up on the time delay. Speed reductions in descent should be rare, but possible when reducing speed due to turbulence in clouds. In level flight, we may reduce our speed when entering an area of turbulence. For a A320 we would usually reduce as far as M.76. These are the reasons I can imagine, why we change our speeds.
- Unfortunately, we cannot be of much help on this request as we still utilise procedural control for all our controlled airspaces. While we do have a surveillance tool for the oceanic environment, the only time we ever deal with speed controls is when effecting mach number restrictions in conjunction with reduced separations based on RNP4. This is only limited to ADS/CPDLC capable aircraft. For the approach/departure environment, the only forms of speed control we use are based on vertical speed i.e. rate of climb/descent. Speed restrictions are as per the International Civil Aviation Organisation (ICAO) designations such as 250KTS below 10000FT etc.
- I can only provide comment from a Business Jet perspective. As you are probably aware we do not fly cost indexes as the airlines do but similar to the airlines with ever increasing fuel prices we are driven to fly at most fuel efficient speeds. In the past there was a trade off between fuel and time/ maintenance costs; however in today’s environment fuel costs are so high that fuel efficiency is always the major factor unless trying to make up for lost time to meet a landing slot. From the fleet of business aircraft we operate there are typically 2 climb and descent profiles available so depending on the operator just on one common type ATC could be faced with varying speeds not to mention the variation in speeds amongst different aircraft types. On descent we often encounter requests for high or low speed descents at a fairly late stage which can lead to high fuel burns. If possible an early notice of an expected profile speed would help in making for an economical descent. Possibly ATC should acquire climb and descent speed ranges for aircraft types and when required issue such speeds; this would obviously increase ATC workload. As more VLJ (Very Light Jets) come to market this will increase the problem.
- (Our) airplanes are quite capable of various speeds to meet needs of the operators. With high fuel prices many airlines are adjusting cost indices and cruise speeds to reflect this increased cost. Since the operators have very unique needs depending on fuel costs and leg segments, any discussion of standardization of speeds or improved spacing awareness needs to be addressed to/with the operators.
- I have spoken to our FDM guys and they promised me to create a set of statistics, which will show the average speed schedules of our aircraft actually flown. In the mean time I can offer you what our books say. As (our) policy 250 KIAS is flown whenever flying below FL 100. Exceptions are very rare and usually on ATC request. Avro RJ100 - Climb 260-280 KIAS/ M.64 - .66; Cruise M.67; Descent M.67/270-290 KIAS Airbus A320 Family/A330/A340 - usually Econ speeds are flown (cost index) but optimum speeds are 300KIAS/M.78 (A330 M.80) during climb and descent. The speed range for CI is appr. 270-310 KIAS. These speeds may be quite a bit lower if the CI is set to zero, which may be done if the flight is early e.g. due to strong tailwinds. As soon as I have more info I will forward it to you.
- The original (message) also mentioned the problem of differing speeds flown across the Atlantic. Given that these are flight planned in advance and that our crews will fly the allocated speed in the Oceanic clearance, I would have expected this to be easily controlled by the ATC units. If there is evidence that crews are not flying speeds allocated in the clearances or revised clearances then the airlines can deal with it, but I was not aware that this is an issue, so it must simply be the mixture and variety of speeds. Clearly for the airline the speeds filed are at the planning stage and will result in best fuel savings and maintaining the schedule as mush as possible dependent on wind conditions. This may change during the actual departure due to delays etc. and the crew then decide on requesting something different in regard to speeds, however as the allocated speed and assigned flight level is coordinated by ATC, I would have thought that the structure would allow similarly planned speeds to be allocated the same tracks and FLs. The introduction of a 250kts speed limit below FL 100 in the London TMA has worked very well over the last year or so. Anything that reduces holding and controls this aspect would be welcome and if reducing speed in descent helps this in any way then it should be encouraged.
- You are correct and I can imagine with the fuel costs as high as they are, most airlines are now flying according to CI which gives a much lower, than what was previously normal, climb and descent spd. For descent, I have instructed our crews to transition to and maintain 290kts if required by ATC to maintain the arrival sequence
- With fuel costs on the rise, one of the main priorities is to minimise the burn by flying the most fuel efficient speed, not only in the cruise but also climb and descent. FMC Cost Index based speeds are used to fly the most efficient speeds based on crew, fuel, maintenance and other costs. As fuel prices are so high, this dominates the CI calculations and therefore the speeds. Our current speeds for the 757/767 are approximately 290/.785 for the climb, .785 for Crz and 260kt for the descent. If ideal CI speeds cannot be flown due to ATC constraints and the aircraft has to be slowed down using additional drag or has to accelerate using additional thrust, much of the fuel saving achieved by CI speeds will be lost. Having discussed this issue with UK NATS last week, it appears that a standard descent speed of 270kt may be introduced in the London area and perhaps introduced to the rest of the UK at a later stage. In the short term, if “free speed” is not available, the key to achieving a sensible compromise is to inform pilots of the expected descent speeds before the descent is started. This allows pilots to re-program the FMC which will then re-calculate a revised idle Top of Descent point.
- We fully support the opinion stated in this previous response (number 13)
- About speed ranges, we are having some problems at (our) TMA because of the very different speeds at which different traffics intercept and follow the localizers, especially in our South configuration, as the traffics have to follow the localizer for nearly 20NM on than configuration. Most operating companies especially (our national) ones tend to maintain high speeds (of) around 200 knots to nearly 6 DME, while some other foreign companies not used to the local conditions, tend to reduce (as much as 160 NM on 20 DME of the localizer) even if instructed not to do so. This has lead to very difficult situations in trying to maintain separation along the localizers, specially as the approaches to the two parallel runways 18R and 18L are dependent and so if one traffic reduces on its localizer, it doesn't affect just it's localizer but also the sequence on the other localizer. On the other way as the profile to that approach is quite steep, some other pilots report they cannot reduce under 190 kts351.88 km/h <br />97.66 m/s <br />. The solution it's not easy as on final approach the operation depends on pilots and not on ATC, if they report they cannot comply with a speed restriction is little left to be done apart from taking that traffic out of the localizer and try again. Why some can comply and some others not on the same situation is as difficult to tell as why some cross clouds areas and some others not, a fact that is also quite annoying on heavy saturated terminal areas when weather conditions are bad.
- With the cost of oil reaching USD $140 a barrel this weekend, the major Australian carriers have announced that they are ‘assessing’ the fuel burn efficiencies that can be gained by reduced operating speeds. If there is a company specific policy then that is something that can be relayed to ATS and catered for at the system level. I have a personal concern that a number of well meaning, but uncoordinated aircrew may well attempt to experiment with fuel burn strategies. If this occurs, then some unsuspecting ATC’s may well be embarrassed by unexpected speed reductions.
- I can appreciate the severity of this issue on traffic separation, and agree with the analysis provided as it suggests an effort at more fuel efficiency using cost index. As the optimal speed is driven dramatically by aircraft weight, it is certainly no surprise that the mix of aircraft results in this problem. I believe most operators will cooperate with speed assignments, even though we prefer to seek our own optimum solution. Please advise if we need to do anything differently.
- Cost index climb is strange given that a lower cost index may require a faster climb to get to cruising altitude and then enjoy lower fuel burn associated with slower speeds. As for the same type, some companies will operate differently to others. Different engine ratings with same engine types, different payloads, different company policies. Fuel prices are dictating major changes in flight planning and we in constant review of our planning. It's a complex area and the airlines are doing their best given the situation.
- According to PANS-OPS, operators are requested to inform the ATC should they change the speed by more than 5% compared to FPL speed. (We) always inform ATC immediately of any changes. However, ATC appears not to react and this could add to the frequency of further congestion. The French DSNA has verbally informed (us) that such notification may now not be necessary any more under radar controlled areas. The reason is that development in technology means that the ATC should already have systems in place that can detect small changes in speed very accurately. Would it not be better to waive the need to inform ATC when speed changes occur below 15% (or at least 10%)? (We) could then file for example 270/M0.73 in FPLs and this would cover 230 to 310 / M0.65 to M0.82.