# Why does my airliner turn the engines way down about 3 minutes after takeoff? **URL:** \ **Category:** Factual Questions\ **Created:** [July 15, 2005, 3:08am UTC](https://boards.straightdope.com/t/why-does-my-airliner-turn-the-engines-way-down-about-3-minutes-after-takeoff/312612 "2005-07-15T03:08:42Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [July 15, 2005, 3:08am UTC](https://boards.straightdope.com/t/why-does-my-airliner-turn-the-engines-way-down-about-3-minutes-after-takeoff/312612/1 "2005-07-15T03:08:42Z")
I fly a lot on business, and I’ve always noticed this on takeoff; the engines spool way, way up and we go blasting off the runway. Then, about two to five minutes in, at altitude but still climbing, and after the flaps/wing extenders have been retracted, the engines spool way down. Then they go back up, not as high as before though. I can understand why you’d bring the engines back a bit when you want to level off, but why drop them way down, then raise them again? ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [July 15, 2005, 3:12am UTC](https://boards.straightdope.com/t/why-does-my-airliner-turn-the-engines-way-down-about-3-minutes-after-takeoff/312612/2 "2005-07-15T03:12:21Z")
Noise abatement procedures? ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [July 15, 2005, 3:26am UTC](https://boards.straightdope.com/t/why-does-my-airliner-turn-the-engines-way-down-about-3-minutes-after-takeoff/312612/3 "2005-07-15T03:26:34Z")
> [@RickJay](#): > > I fly a lot on business, and I’ve always noticed this on takeoff; the engines spool way, way up and we go blasting off the runway. Then, about two to five minutes in, at altitude but still climbing, and after the flaps/wing extenders have been retracted, the engines spool way down. Then they go back up, not as high as before though. > > I can understand why you’d bring the engines back a bit when you want to level off, but why drop them way down, then raise them again? How long after throttling down do they start bringing them up again? If it’s right away, it might be that they pulled way back to loose a bunch of thrust they didn’t need, and then were slowly pushing the engines back up to get the kind of thrust they wanted. I’m not sure how turbofans work, but I’ve heard of turbine engines having a lag between a throttle adjustment and the engines responding, so this could be due to that (assuming I wasn’t just plain told wrong about the lag) ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [July 15, 2005, 1:29pm UTC](https://boards.straightdope.com/t/why-does-my-airliner-turn-the-engines-way-down-about-3-minutes-after-takeoff/312612/4 "2005-07-15T13:29:56Z")
You’re referring to Toronto Pearson, right? **mks57** has it - noise abatement procedures are in effect there. [The Greater Toronto Airport Authority]([www.gtaa.com/documents/community/](http://www.gtaa.com/documents/community/) noise\_management/managingnoise.pdf) says: > [@](#): > > Noise abatement procedures governing flights out of Toronto Pearson are approved by Transport Canada and are legally binding on aircraft operators. **Departing jet aircraft are required to throttle back from takeoff power to less noisy climb power shortly after takeoff and must follow specified headings or groundtracks to 3,000 feet above airport elevation before making en route turns.** Propeller aircraft must comply with jet procedures between11:00 p.m. and 7:00 a.m., except regarding climb procedures. During the day, they may turn as low as 500 feet above airport elevation to accommodate increased hourly operations. > > Arriving jet aircraft at all times of day must remain at 2,400 feet above airport elevation until they line up with their runway. They must then maintain a three-degree glide slope approach until touchdown, and minimize noisy reverse thrust after touchdown. While aircrew act to minimize noise during departure sand arrivals, sometimes they may have to deviate from noise procedures if there is any question of safety. The GTAA continues to work to minimize disruption from aircraft noise.