How Much Thrust % Does A Plane Have While Taking Off and Landing?

For the average Boeing 747-400, how much thrust does the plane have at takeoff (eg. 75%) and how fast is the plane going at takeoff?

For the same plane, what would the same circumstances be for landing?How Much Thrust % Does A Plane Have While Taking Off and Landing?TO thrust is based on a number of things nowadays. Reduced thrust is used almost all the time to save money and engine wear. Density altitude and runway parameters (length, slope, wet/dry) combine to give an EPR setting and set V1 and the other speeds. On the 737, I've seen as low as 65%.



Landing speed is based on weight and flaps setting, which typically doesn't vary (although at my airline we used more flaps for CAT III approaches for better runway visibility).How Much Thrust % Does A Plane Have While Taking Off and Landing?On any takeoff, a transport airplane must be able to abort the takeoff on the remaining runway, or if an engine fails at the most critical point during takeoff, the airplane will be able to climb away from the airport at a minimum climb gradient and clear all obstacles up to 1500 feet.



Takeoff thrust is set to meet or exceed that requirement, considering aircraft weight, airport temperature and elevation, runway length and slope.



Taking those conditions into account, the thrust is determined by a computer, or charts, graphs or tables, depending on the airplane. We have no flight deck correlation between takeoff power settings and pounds or percentage of thrust developed, and it is unusual to use 100% thrust for takeoff.



Takeoff speeds for a given runway and atmospheric conditions will vary with weight. At normal takeoff weights (145,000 lb), the MD80 rotation speeds are in the 145 ish knot range, but with high temperatures and high weights, it can be 160 knots.



Landing speeds are based on airplane weight, surface winds and gusts. For the MD80, the no wind landing speed is based on landing weight and airport elevation, and is adjusted for winds by adding half the steady state headwind and all of the wind gust speeds up to a maximum of 20 knots.How Much Thrust % Does A Plane Have While Taking Off and Landing?As Jimmbo and Warbird... have said:



On takeoff, anywhere from about 75% to 100%. The maximum reduction allowed is 25%. Low altitude, cool day, long runway will almost always be 75% while high altitude, short runway, obstructions in the takeoff flight path, contaminated runway, inoperative components, etc., may require full blower.



On landing, the engine must be spooled to some number that guarantees immediate thrust in the event of a go around or sinker. I am making a WAG here, but I'd bet that the number for landing is around 30%. We use N1 to determine that the engine is spooled, but that doesn't tell us the actual percentage of power. As for reverse thrust, some airlines suggest idle reverse and some don't; irrespective of the recommendation, some captains use idle and some use full reverse. I've never looked, but I'd bet that full reverse is only around 50-60% of the thrust.



One note is that the percentages used above have nothing to do with percent N1, N2, or N3. It is a percentage of thrust, and we have no way in the cockpit to actually know what actual percentage we are using unless it is full power. Reduced thrust is derived by using an assumed temperature. In other words, based on the performance planning system, on a 30 degree day, we might tell the engines to produce power is if it were a 90 degree day. Different airlines, makes and models use different methodologies to accomplish this.How Much Thrust % Does A Plane Have While Taking Off and Landing?
One note to these good answers, the aircraft operates in two modes, "ground mode" or "Air Mode." When the landing gear shock struts extends during take-off, the aircraft recognizes that it has entered the "air mode".



It gets this information from proximity switches in two locations....the nose gear strut and one of the main gear struts. Whether the aircraft is in ground mode or air mode affects LOTs of systems, but for the context of this question the system that is affected by the aircraft switching to air mode is that the engines will go to "flight idle", a higher RPM in the air.



We test this on the ground by tricking the aircraft into thinking it is in the air and we can see and hear the engines spool up. So on approach to landing, even though the pilot has pulled the thrust levers back to the idle stops, the engines are actually spinning faster than they would be on the ground. I can't remember all the reasons that this was designed into the engine systems, but one of them is engine flame-outs when flying through heavy rain. With the engines running a tad faster there is less chance they will flame-out if the pilot pulls the levers back to idle to dump speed during landing in heavy rain.



It would be a good discussion for another question but one other thing that happens when the aircraft goes to air mode is that the cargo door opening system is deactivated. A United Airlines 747 had it's door open in flight by the normal system, due to a short circuit that activated the opening circuit. Ever since then, the door circuit has been deactivated by going to the air mode so even if it did short circuit in flight, there would be no power to the system.