I’ve known since the beginning that the Waypoint Hypothesis is at the edge of the B777 performance window for what we know as facts about the flight of MH370. The Waypoint Hypothesis assumes a deliberate act designed to disappear MH370 in the remotest section of the SIO possible. To do that, you fly fast and high and straight (as opposed to curvy) and relatively fuel efficiently away from land. In other words, you fly like a typical airliner would, but with less constraints. A simple motive hypothesis matches up with data. Indeed, to make it to the Waypoint Hypothesis point with the known fuel available, no other type of options are possible – it simply could not have made it there. It’s uncanny that the fuel range circle meets the 7th arc exactly at the Waypoint Hypothesis endpoint. It’s as if hypothesis were predicting actual data and vice-versa.
Between 2014 and 2018, I considered the Waypoint Hypothesis as superior to other hypotheses of a flight termination further north because the above simple human factor motive is in accordance with Occam’s Razor (the simplest hypothesis is likely the correct one). Yet mathematic data analysis always encouraged the hunt further north, first from analysis of the satellite data, and later analysis of the recovered debris drift data. Human Factors or motives have not played into the official search effort in any significant way.
In 2018, I discovered the official satellite data analysis was flawed, but that a relatively new theory called Bayesian Occam’s Razor could plug that hole. In fact, Bayesian Occam’s Razor possesses the curious property of proclaiming “more ways to achieve a given hypothesis outcome make that hypothesis a less likely.” Bayesian Occam’s Razor is able to characterize the satellite data in a completely new way, according to deep principles. Highly constrained hypotheses, like the Waypoint Hypothesis are more likely to be correct.
Since the early days of jet aircraft and commercial travel, the technique of gradually climbing in cruise altitude as fuel burns off and the aircraft becomes lighter has been widely used by pilots. The altitude that provides the most fuel-efficient cruise (at the desired speed) at the start of a long flight, when the aircraft is fully loaded with fuel, is not the same as the altitude that provides the best efficiency at the end of the flight, when most of the fuel aboard has been burned. This latter altitude is usually significantly higher than the former. By climbing gradually throughout the cruise phase of a flight, pilots can make the most economical use of their fuel.
The most fuel efficient step-climb would actually be a continuous one. The Concorde reportedly used a continuous climb because it flew so high it didn’t have to worry about other traffic. But 777 and other conventional airliner pilots (even autopilots) don’t just execute a step climb on their own, they coordinate with Air Traffic Control (ATC) that the climb level is clear and then execute it.
A 777 pilot’s description of the step-climb procedures and quirks in a 777 is especially helpful:
The FMC schedules step climbs throughout the flight based on the settings in the Cruise Altitude (CRZ ALT), Step Size (STEP) and potentially Step To (STEP TO) fields based on the aircraft weight, actual/forecast wind and temperature data and speed schedule (usually cost index). Additionally climb steps can be placed on the LEGS page of the FMC to schedule climbs at geographical waypoints in the flight plan, rather than the optimal weight/speed/wind schedule predicted by the FMC. What this all means is that for a long flight the FMC assumes that you will be able to increase your altitude as the flight proceeds, and calculates ETA and Fuel at Destination accordingly.
Long haul pilots tend to be pro-active about climbing and often seek climbs prior to the recommended step climb point. This is usually in an effort to avoid being blocked from higher levels by the increasing numbers of other aircraft on the more common routes. If you can get up there earlier, you’re more likely to be the one blocking, rather than finding yourself blocked from those fuel saving altitudes. Do it too early though and you’re punishing yourself, with deviation from optimum altitude typically being a 2:1 ration against being high – that is, you are approximately equally less efficient being 2000 ft above your optimum level as you are being 4000 ft below it.
In any event – Since ideally we probably don’t want to run an entire NNM checklist everytime we pass a step climb point without actually starting a climb, there are now several unofficial habits I’m seeing creep in that are being driven by the inclusion of this checklist. This includes manually setting a step climb point a waypoint or three down route while you wait for a clearance to climb.
As far as what the typical step climb is for a 777:
It is not true to say a typical Boeing 777 profile has a constant altitude segment. Perhaps the profile you mentioned covers a short sector of a 3-to-4 hours flight where further step-climbs have no economical advantage. I do a lot of long haul flights from the Far East to Europe of around 12 to 13 hours duration where there are at least 3 step-climbs. With a heavy aircraft (around 286,000 kg), the computer calculates the optimum altitude of 31,000 feet initially.
As the aircraft climbs, the computers recommends a step-climb to 35,000 feet when the aircraft weight reduces as a result of fuel burnt (a Boeing 777 consumes around 6000 to 7000 kg of fuel per hour depending on the
Three quarter way through the flight when the aircraft is about 55,000 kg lighter because of the fuel consumed, the computer will recommend a further climb to 39,000 feet. Looking at this climb profile, it is not true to say that a typical Boeing 777 has a flat segment from the top of climb to the top of descent.
There are a few answers to questions, certainly knowable, that I have not seen discussed in relation to MH370:
- Certainly step-climbing is a typical feature of typical commercial flights, but what are the implications of it for MH370?
- The optimal step-climbs computed by the FMS depend on having relatively current weather data. When and where does the FMS obtain this data? Is the FMS only loaded with a small slice of wind data along the filed flight plan prior to departure or is this data broadcast?
- It appears step-climbs can be pre-entered on the LEGS page. Does the pilot have to manually accept them at the time of execution? This has implications for whether the pilot would have had to be alive for the duration of the flight.
- The FMS will automatically recommend step climbs, but is a step climb profile viewable for the entire flight ahead of time? Would it compute increasing climbs to complete fuel exhaustion?
I would certainly like to know if a step-climb could be fully automated to a high-altitude fuel exhaustion without further pilot input, as well as whether the perpetrator(s) could have had wind data for the actual flight path. Given the typical nature of step-climbs described by one of the pilots above, it’s possible an experienced pilot might just enter a typical step climb by “feel” after observing hundreds of them, rather than rely on the FMS to compute it. This could be particularly true if that meant one did not have to depend on correct weather data or having to wait around for the FMS to recommend a new climb. Whether a pilot had to remain alive to execute an FMS-recommended step climb or a manual “guessed” one is important for end-of-flight.
An interesting possibility arises if it was possible to have accurate wind data and preprogram the FMS to execute optimal step climbs. We could presumably know nearly exactly what the climbs would have been, if the wind data for March 07, 2014 is recorded.
How much fuel does step climbing save?
This information is a little hard to come by, but a Boeing Engineer gave a presentation that generically, it is on the order of 4% on a four-hour flight. The amount saved depends on how far off optimal altitude one is and how long the flight is, as well as the actual winds at altitude. Note the figure indicates more savings as the flight continues, but this is only because the optimal flight level keeps getting higher.
This is definitely in the ballpark of what is needed to close the gap and match fuel usage exactly for the Waypoint Hypothesis. This would mean a hypothesis developed long ago just so happens to have predicted the exact fuel exhaustion at the 7th arc and pending a check, could match BTO satellite data the best of any hypothesis.
It seems uncanny, but perhaps it is simply Bayesian Occam’s Razor at work. Simple, and likely correct, highly constrained hypotheses typically make predictions. Of course a hypothesis that is correct would make uncanny predictions about the data too, if you didn’t know it was correct. Although I believe I have demonstrated that no step-climb is needed to make it to the Waypoint Hypothesis point, a step-climb would possibly close the apparent slight fuel shortage gap and make available fuel match the path perfectly. A step-climb is a perfect fit with the motive and would something a typical pilot would do. It simply fits very well.
I hereby predict that a step-climb is involved in the disappearance of MH370 and the flight data recorder will show it – of course that presumes MH370 is found at 40S, but that is the most likely single spot. It will take a lot of analysis to verify the above all works, but I am confident it will, given the substantial likelihood the Waypoint Hypothesis is correct.