# Why wouldn't a plane start its take-off run from the very beginning of the runway to keep the option to utilize the full runway if necessary?

I was just watching BSL/LFSB on Flightradar24 and noticed that flight W67772 didn't start its take-off run from the end of the runway.

Wouldn't it make sense to start every take-off from the end to have more runway available in case you need it (for whatever reason)?

Airlines (operating multiengine airplanes) calculate the necessary takeoff distance in consideration of the potential for an aborted takeoff occurring at the most disadvantageous point (during the takeoff run) and being able to stop on the remaining available runway.

These performance calculations also consider the rare possibility of an engine failure occurring at the most disadvantageous point in the takeoff run and thereafter be able to continue the takeoff, become airborne and clear all obstacles during the initial climb.

The total length, from the very beginning of runway 33 (used by flight W67772 shown in your question), is 12,795 feet (3900 meters). This is a very long runway.

The runway distance required in taking off from the intersection (as shown in your question) would have been calculated considering the factors mentioned above (along with some additional factors, such as outside air temperature [OAT], runway condition [dry/wet], wind, pressure altitude, aircraft weight, etc.). Obviously, the calculated performance requirements for that flight (an A321, I believe) did not require the use of all 12,795 feet of available runway.

There can be some advantages using an intersection-reduced takeoff distance instead of using the entire length of available runway. (Sometimes) less fuel is burned and total taxi and flight time are shortened, to name a couple of advantages. For the flight mentioned in your question, there could also have been some taxiway or runway maintenance ongoing that might have required the use of an intersection takeoff.

The considerations for "light" general aviation aircraft doing intersection takeoffs, is generally based on an entirely different set of factors and not considered in my answer (since your question addressed the operation of an air carrier).

• As an airline pilot working for a major European airline I can testify that we regularly aim/plan to take off from intersections. We run the performance figures for intersections and will typically request from ATC to use an intersection if the cabin is secure for takeoff. (It is often the lack of cabin secure which prevents us from taking a planned intersection - cabin not ready so we “might as well continue” to the next intersection/runway endpoint). The goal is operational efficiency - mostly time, but also fuel savings. Jun 1, 2023 at 20:16
• I'm not a pilot, so if I'm reading that map correctly, I'd be very surprised. But does the point where the line changes from white to green represent the actual moment of takeoff? If that's the case, that short bit of white line may be all the plane needs for takeoff, and the fact that the green line continues to follow the rest of the runway may be just a precaution? Jun 2, 2023 at 13:35
• @DarrelHoffman The actual take-off roll would take on order of 5,000 ft, so the green line definitely starts before that. It indicates the point where the transponder started reporting altitude, but that might be triggered by speed. But it did certainly continue straight after rotation. I wouldn't call it precaution, because there is no way to land back on the remaining runway with a jet, but it keeps things simpler while the pilots are busy with other tasks like retracting gear and flaps. Jun 2, 2023 at 22:17
• @JanHudec and Darrel: As well as reducing pilot workload, flying straight is safer: the thing that makes engine failure after takeoff extra dangerous is that you have so little energy (altitude and speed^2). Turning hurts climb-out performance, so doing it too early would keep you lower and slower for longer. And makes a stall more likely if something goes wrong at lower speed, and more dangerous at low alt. Or if something weird happens the first time the plane banks, you'd rather that be at 500 ft than 50 ft. I assume there'd also be noise considerations for what you're flying over. Jun 3, 2023 at 13:10

Operational efficiency - significantly, you have saved time, and you might also save fuel from an unnecessary longer taxi.

1. Operational Efficiency:

As discussed above, taking off from an intersection saves taxiing time. If you save this on two occasions during the day, you have saved 10 minutes. This might even mean the difference between missing an ATC slot restriction on your third sector later in the day. Remember, many major short-haul carriers seek to turn around their aircraft in less than half an hour. Minutes matter.

2. The takeoff is still completely safe from the intersection:

The aircraft in your question took off from the D intersection at LFSB/BSL.

From Intersection D: 2900m/9514 ft Takeoff run available (TORA) Full RWY 33: 3900m/12795ft TORA

Here are some performance calculations for a 737-800 (reasonably analogous to the aircraft in your question), loaded with (a typical sort of flight) - 7 tonnes of fuel, 175 adult pax on board, and 700kg of baggage in Hold 2. The performance figures are from the approved source for LFSB/BSL: wind calm, 15 degrees Celsius outside air temperature, dry runway, and 1013 hPa QNH.

• Intersection D: De-rate to 24k, using assumed temperature thrust reduction (known as Flex for other types) of 41 degrees C, v1 140 kts, Vr 141 kts, V2, 145kts
• Full RWY 33: De-rate to 24k, using assumed temperature reduction (known as Flex for other types) of 41 degrees C, v1 140 kts, Vr 141 kts, V2, 145kts

From the data above, you can see that the aircraft will be set up identically for takeoff from runway intersection D or if it were to take off from the full runway.

So, in this instance, the further taxi from intersection D to the full runway would be around 1km (cf. airport charts) or perhaps around 120kg of fuel burnt. This may not sound like much, but if that airline operated 2000 flights per day, then it is a saving of almost 250 tonnes of fuel - costing perhaps around 200,000 \$US, in just 1 day.

Please note that there may be circumstances where higher (or "less" de-rated) performance is required when the takeoff run is shorter from an intersection, which would potentially lead to higher fuel burn on the takeoff roll or more wear on the engines.

3. Takeoff safety for jet aircraft is arguably less about runway distance available and more about critical decision making around speeds close to V1.

Taking off from intersection D gives you a takeoff run available (TORA) of 2900m. To put that into perspective, the TORA at Bergamo runway full length is 2874m, TORA in Faro full length is 2490m, TORA at London Luton, both runways full length is 2162m (and on a hill), or finally at Bristol, where the TORA is 2011m (and on a hill). All these airports have a TORA less than that available from the D intersection at LFSB/BSL and are frequently used by jet aircraft without any concerns over safety.

At v1 speed of 140 knots, a 737 would travel the distance between the D intersection and the full runway length (1000m) in 13.89 seconds. (And 1000m is a large difference in length between intersections). Perhaps a more average distance between intersections is 400m, which gives crew another 5.56 seconds of decision time (really not much)…

Arguably what is therefore more critical from a safety perspective is not necessarily the increased runway available, but rather the decision making skills of the flying crew. If the aircraft was unsafe to takeoff the crew need to decisely act before v1 to reject the takeoff.

Furthermore, if the worst eventually happens (aside from a dual engine loss at v1), such as a major engine damage or fire at v1, the aircraft is still safe to fly - and flying crews regularly train for this scenario. It can actually be safer to get the aircraft into the air, secure the engine and return as opposed to stopping or trying to immediately land it back onto the runway.

As an airline pilot working for a major European airline I can testify that we regularly aim/plan to take off from intersections. We run the performance figures for intersections and will typically request from ATC to use an intersection if the cabin is secure for takeoff. (It is often the lack of cabin secure which prevents us from taking a planned intersection - cabin not ready so we “might as well continue” to the next intersection/runway endpoint).

Wouldn't it make sense…to have more runway available

Safety is priority, however operational efficiency is also a priority. The takeoff is safe from the intersection: now we think about saving time and fuel.

• 41 degrees c might be a bit high estimate for basel in May, but great answer. I appreciate that a high temperature estimate will only mean you get better performance at a lower realistic temperature - do you really high estimate on purpose?
– Jamiec
Jun 2, 2023 at 13:53
• @Jamiec 41 degrees is the assumed temperature under the assumed temperature thrust reduction method for the engines (Can be known as Flex for other types). The Outside air temperature used is 15 degrees in Basel. Cf. b737.org.uk/assumedtemp.htm Jun 2, 2023 at 13:55
• cool. I learned something else new today!
– Jamiec
Jun 2, 2023 at 13:57
• Wait, they burn 120 kg of fuel for 1 km of taxi ? That's approx 1.5% of the 7 tons you took as an estimate. What an amazing figure. Jun 3, 2023 at 12:23
• @PhilippImhof: Yeah, jet engines are more or less constant thrust, not constant power, over a range of speeds, and power is force * speed, so the amount of useful power per fuel used at taxi speeds is very low, and the total fuel burn adds up to significant greenhouse gas emissions. (Pushing on the ground instead of a large amount of air would be way more efficient, that's why cars power the wheels). Jun 4, 2023 at 17:33

As an example:

I did my flight training at Boeing Field (KBFI), which has two runways: a GA runway that is 3,700 feet long, and a commercial runway over 10,000 feet.

My flight school was near the middle of the commercial runway, so we frequently would taxi to intersection A9, and have nearly 5,000 feet of runway in front of us, whether taking off to the North or South. (Note that 1/2 of the Commercial Runway is still more than the full length of the GA runway, and also closer to the flight school parking area)

5,000 feet is a LOT of space for a training Cessna. The time and cost involved in taxiing to the full end of the runway was considerable, but really provided very little extra safety margin. 5,000 is already enough to recognize a bad take off and safely reject it, especially since most flights had an experienced CFI on board.

This is one clear case where it definitely makes sense to take off from the middle of the runway rather than use the full length.

Another example is at Johnson County Executive (KOJC) in Kansas, where taxiway Bravo goes almost, but not quite, to the end of runway 36.

To get the true end of the runway involves crossing the runway (with Tower clearance), and taxiing a bit further on taxiway Alpha. That is extra complexity and ground driving, to get an extra 400 feet (approx) of runway.

A lot of planes choose to just request an intersection departure from "Bravo at Juliet" rather than "Cross 36 at Juliet, Join Alpha, Continue Taxi to 36". They'll still have roughly 3,600 feet in front of them, which is still plenty of space for a safe takeoff or rejection.

• So that's why they casually send trainers to B4 to go south. Jun 1, 2023 at 14:50
• by way of comparison, my home field has about 1,900ft - so yeah 5,000ft is a huge amount.
– Jamiec
Jun 1, 2023 at 14:52
• Yes, that makes sense of course. :) What you're describing makes sense for the training Cessna: the runway length is way oversized for its requirements, if I understand you correctly. But are city airports (like BSL/LFSB from my example) just as oversized for jets, too? I looked up the airport map and by starting take-off from that intersection, runway length was reduced from about 3.9 to 2.9 km. So where could I find out the required distance for an A321 which aborts take off juuuust before V1? Jun 1, 2023 at 16:33

There's nothing more useless than fuel you left on the ground, or runway behind you.

We're generally taught to use all the runway, as you point out; why wouldn't you? What if you need it. However for the sake of expediency pilots may plan for, and request, take off from the intersection of the taxiway and the runway.

Flight W67772 looks like it was operated by an A321 from Basel. One must assume that there was plenty of runway available, including whatever contingency was required by Wizzair's SOP, to take of from that intersection.

• Hmm, can you explain who would ask for an "intersection takeoff" and why? Is this basically a case of "We'd either take off long before runway ends or decide to abort and even then we'll still have more than enough runway left even if we don't start take-off from the very beginning"? Is the BSL runway that long compared to other airports or is this usual practice at all airports? Jun 1, 2023 at 14:09
• @CannedMeatLover is that clearer?
– Jamiec
Jun 1, 2023 at 14:29
• @Jamiec, the other useless thing is a half a second ago! Jun 1, 2023 at 16:18
• @Jamiec - As an airline pilot working for a major European airline I can testify that we regularly plan to take off from intersections. The premise of your answer assumes that it is ATC prompting crews to use intersections which is simply not true - at least not in my experience across Europe. We run the performance figures for intersections and will request from ATC to use an intersection if the cabin is secure for takeoff. The goal is operational efficiency - time and fuel burn. We have already proven that the takeoff is safe from a performance perspective. Jun 1, 2023 at 20:10
• @tedioustortoise thanks for the insight, ive updated my answer. Flying light singles we sometimes get asked at larger airfields whether we can "accept an intersection departure" and I just assumed that was the same for the big guys. Again I sort of assumed pilots would have run the numbers knowing full well the likeliness of that request.
– Jamiec
Jun 2, 2023 at 7:50

Clearly, the answer is yes. The OP asks, at the ending of their question -

Wouldn't it make sense to start every take-off from the end to have more runway available in case you need it (for whatever reason)?

This answer was offered previously regarding a similar consideration to the posted question. The gist of that answer, which is relevant here, was summarized in the last paragraph of the introductory to the NTSB accident report, which is as follows...

The circumstances of the accident are consistent with the pilot failing to maintain sufficient airspeed following a loss of engine power during takeoff, resulting in the airplane's wing exceeding its critical angle-of-attack and a subsequent aerodynamic stall. Instead of using the full runway length of 6,179 ft, the pilot elected an intersection takeoff with about 2,570 ft of available runway. Calculations showed that, had the pilot used the entire runway for takeoff, sufficient runway for a landing following the loss of engine power would likely have been available.

Nevertheless, I am reminded by an executive pilot I know who has 12k+/- logged flight hours, "Tom, if the available runway is 17 thousand feet long, and only 1700 feet or a bit less is needed at full power to become airborne at the current density altitude, then a midfield departure using 8500 feet of runway is in order rather than a taxi all the way to the end of the runway, given all other things considered." In that case the answer is no. Hence the relevance to the answer provided by Jamiec, there is no need to unnecessarily consume fuel on the ground given adequate available runway for a midfield departure. Specifically, the issue here must be viewed in regard to the situation faced by the pilot, and the resources available to the pilot upon takeoff. Hence, "why wouldn't" depends conditions at the time, namely meteorological conditions, physical availability of runway, and performance of the aircraft.

• The question asked (in the title) is "Why wouldn't..." - not a yes/no question, while the question asked within the OP is "wouldn't it make sense to start every takeoff from the end...". Given your (excellent) example of the 17,000' runway case, the answer you write seems to contradict your first sentence.
– Ralph J
Jun 1, 2023 at 22:52
• Ah, I see your direction. The offered edit should clarify the "Why wouldn't..." qualifier. No problem... Jun 2, 2023 at 0:30