# Tag Info

77

It is normal for engines to spool up during the approach. The initial part of the approach, from cruise level down to approximately 10 miles from the airport, is flown at flight idle power. This is the most efficient way to get down. In the final part of the approach, flaps and landing gear add so much drag that the engines need to be well above idle power. ...

55

This is called Powerback, most aircraft can do it, but it is not done very often. In a jet aircraft, the three main problems are: Reverse thrust tends to throw a lot of debris into the air because the exhaust is deflected to the sides and up and down too. This debris can damage the engine itself, other things on and around the aircraft or injure someone on ...

36

I wouldn't worry to much about the mass of the engine. That's actually not the biggest problem. Instead, I'd be scared far more by the angular momentum. That turbine has a large moment of inertia and also a higher angular velocity.To flip it, you have to reverse the angular velocity. It's essentially flipping a gyroscope, but this is a gyroscope weighing ...

36

Four reasons among many others it's not possible: Weathervaning effect from the vertical surfaces of the tail would turn the aircraft as it accelerates, the tail would not remain upstream of the nose. Taking off requires the engines to deliver their maximum power and the wing to convert this power into lift very efficiently to leave the ground. The poor ...

29

Why doesn't the A380 use its outboard thrust reversers? Because it doesn't have (or need) any. The A380 has reverse thrust on the inboard engines only. This saves weight and since the outboards are often way out over the edge of runways, decreases the risk of FOD. From Airliners.net Like all certified transport aircraft of this type, the A380 can stop ...

29

The brakes are much more effective than anything else, at least for the jet I have experience in (EMB-145). Our landing performance data typically assumes full braking application, spoilers deployed and no reverse thrust. The airplane will most certainly stop without using reverse thrust, just not as fast. I never tried not using the brakes, and if I ...

29

A minimum max reverse power speed is often an airplane operating limitation. It's mostly related to FOD (mostly sand grains and small gravel) and on some designs there may be compressor stall issues due to flow disruptions. On the CRJ 700 max reverse is limited to 75kt although you can use up to 60% N1 down to zero speed. On a 900 you have to be at idle ...

28

The engine does not move, the air flow is only redirected. The method of redirecting the flow varies with the size, configuration, and manufacturer of the engine. The flow does not need to be directed completely forward; the flow is generally mostly outwards and partially forward. This is still enough to create significant drag and slow the aircraft down. ...

28

The biggest problem is that thrust reversers take time to move. During that time they are still producing reverse thrust (even if only at idle) and slowing you down. They must all completely close before you get forward thrust and can add power to start accelerating again. Then, what happens if they don't stow, or only part of them stow? Now you've used up ...

28

In all Airbuses auto-braking system aims for specific deceleration. Once the design target has been reached, the system does not apply more brake pressure although there usually is more available. So, if you apply thrust reverser with autobrake selected it will apply less pressure on wheel brakes and as the target deceleration remains the same, the stopping ...

27

It's not so much that thrust reversers (TRs) are more unreliable than other components of the plane. However, they have a very important impact on the airplane's performance. Hydraulics, flaps, and even engines fail regularly. But engines and hydraulics can be backed up by redundant systems, and an airplane can still land without flaps. But engineers learned ...

26

The question speaks of a very old 747 landing tutorial. And as such I take that to mean it would be of a 747-100/200 aircraft, and that's the reference point I'm answering from. First, concerning the comments below the question that wonder whether you have to worry about unwanted objects on a runway at an international airport, there is no such thing as a ...

22

The problems are two-fold: The airspeed is much higher in flight than when landing, so the thrust reverser doors would have to be much stronger, and therefore heavier to withstand the additional forces, along with the relative wind making them harder to close. What happens when it gets stuck in the deployed position? Now you have to shut down a perfectly ...

21

Even the largest commercial airliners are able to land without flaps, since flap failures do happen occasionally. See a report here where an A380 landed with no flaps. This was at the Auckland, New Zealand airport, where the runway is 3,635 m (11,926 ft) long. The pilots have checklists to follow in the event of issues with flaps, which include information ...

21

Thrust reversal is a complex system (equals money) and it uses significant amount of fuel (also equals money). It is not a very efficient means to reduce the speed of a landing aircraft either, and other methods (e.g. brakes or drogue parachutes) are much better suited. The biggest advantage of thrust reversal is that it cancels out the idle forward thrust ...

21

First drawback is going to be speed of response. The engine is big and heavy, so you aren't going to be able to spin the whole thing around in a tenth of a second. Realistically, it's going to be a few seconds to spin it around. A traditional thrust reverser moves only a very small mass (little flaps, etc), so can react much quicker. Second drawback will be ...

20

There are a couple of reason for the presence of thrust reversers: To reduce wear on the brakes. To provide a margin of safety (for example in wet conditions). In 1995, NASA carried out a survey on airlines Why Do Airlines Want and Use Thrust Reversers?. The results of the survey, though dated, give an indication of presence of thrust reversers. The ...

18

Commercial jets are not designed to use reverse thrust in flight. With engines mounted under the wing, the turbulence can affect the lift over that section of wing. Tail mounted engines could interfere with the tail. This, in addition to the huge increase in drag, is what causes loss of control, as in the incidents that RedGrittyBrick mentions. Speed brakes ...

18

Specific information can be difficult to come by, and each airline may have their own guidance on the subject. I wasn't able to find anything for the 787, but for the according to one 777 crew handbook I found, flaps up landing was not part of certification: All Flaps and Slats Up Landing The probability of both leading and trailing edge devices failing ...

18

During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction This is wrong Reverse thrust does not reverse the rotation of the fan/compressor/turbine. Reverse thrust "simply" redirect the airflow coming out of the turbine in the reverse direction (well, almost, as we'll see in a moment) w.r.t. the ...

18

One concern is Foreign Object Damage (FOD). More reverse thrust means more dirt is thrown into the air, which can then be ingested by the engine: Damage to turboprop engines is not as common as in jet engines, because the inlets are generally smaller and the propeller serves as a first line of defense. Nevertheless, first-stage impeller nicks and scratches ...

17

It can be done, in fact the DC-9 and MD-80 aircraft are approved for backing up using reverse thrust. It is called "powerback". It is rarely used since it is quite fuel consuming, noisy and increases the risk of sucking up debris near the gate area causing damage to the engines. Here's a video of an MD-80 backing up.

17

Short answer The reverser is not installed on the outer engines. As the linked question mentions: This allows to lighten the engines, this also prevents any unwanted and hazardous opening in flight as well as the costly check time for an unused feature. The reverser used on the A380 is a cold flow type. It is merely part of the engine by itself. It is ...

17

We used lots of reverse thrust in the C-130; it was normal to go to full reverse on landing, and also to use some reverse thrust in order to back the plane into or out of parking spots. The two common cautions were oil temperature (on older engines) and dust ingestion / brown-out (on dirt or unimproved runways). On early model engines, sustained reverse ...

16

Perhaps instead of thinking of a single primary means of slowing a large jet, we should think about a primary means for a given set of conditions, the combinations of which are numerous. To mention a few: What is the weight of the aircraft. Passenger aircraft are typically nowhere near max landing weight when they land. Freighters are often loaded such that ...

16

Most modern commercial airliners are prohibited to power back. Ground operations in aircraft fitted with high-bypass engines are usually restricted to idle and low-idle operations (enough to make the craft start moving, after which momentum enables further movement with idle only). Aircraft capable of power back are predominantly thus turboprops, several ...

16

There will be only drawbacks, and some small practical problems such as how does the air stream into the engine when the inlet is facing backwards and we've just touched down at 150 knots. Current thrust reversers achieve about 50-60% of reverse thrust, and the system weighs between 15 and 20% of the engine dry weight. They are very beneficial on wet and ...

15

There are several ways to slow down an airliner: aerodynamic drag friction in the wheel bearings reverse thrust wheel brakes and a few even used a brake chute, but that went out of fashion a long time ago. If the runway is inclined, landing uphill also will slow down the aircraft. Friction and drag you get for free, so I would rely on those first. Since ...

15

Without further knowledge of the procedures/state of the (a) airport, (b) airline and (c) aircraft , I don't think any conclusive answer could be made. To throw some thoughts in: All of Kuala Lumpurs's runways are over 4000 meters long, and braking an A320 (at landing weight) can easily be done without thrust reversers over that distance. Depending where ...

14

This video on YouTube shows a 777 in certification trials, accelerating at maximum gross weight from standing start to $V_R$, then stopping with maximum brake pressure and no reverse thrust. The brake discs are also ground down to the minimum thickness permitted by the maintenance manual to simulate the worst case scenario. The brakes get white hot! Then ...

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