Go Around

[Ophir]

I have been reading about jet engines and just discovered that on approach many jets run up to nearly 90% of thrust due to how long the engine takes to spool up.

What are the go around procedures for many of you big gun pilots? Is the first thing always to go full throttle? What next, clean up the plane?

[Baronman]

I'm not a "Big Jet" operator, but 90% seems a bit high for N1, maaaybe N2....but I think nowadays most modern engines don't take quite as long as the older engines to spool up.

I remember somebody saying that older jets used to approach with the power way up and with lots of bleed valves open so not all of that RPM resulted in thrust.....just my $.02

[Jason]

There's NO WAY you can fly a modern jet at 90% thrust and be anywhere near the correct Vref - you'd be waaaay too fast. As an example in the Challenger 604 at typical weights our thrust setting is usually approximatley 56% N1 on approach - that gives us a speed of about 130 kias or so depending on weight, etc. Keep in mind that in jet engines the range of the engines isn't from 0 to 100% N1. In the Challenger our engines idle at approx. 44% N1 and our 'Max Continuous Thrust' is 97.8% N1.

Go around procedure is the same as in every airplane - Set go around thrust, flaps 20(in the Challenger), positive rate gear up and reaching flap retraction speed flaps up.

Spool times on modern engines are much much shorter than the old engines but it's not 'instant' as it is in a piston. From idle to max thrust in the Challenger I would say is probably 4 to 5 seconds - which can be an enternity if you're in trouble and need to get out of Dodge in a hurry.


Jason

[FlyChicaga]

In our turboprop, we have a fairly short spool up time (in seconds). At the time of go-around, we just call "Missed approach, max power, flaps 7 (or 20)." The PF will push the power levers forward, and the PNF will move the flaps from 7 from 20 (or 20 from 35), then set the power to the GA setting (usually 100% except on hot days).

[C650CPT]

Speaking of Go Arounds ... let me ask you this, what position and at what rate do you push up the power levers on a go around or even on a stall recovery?

I go to what I describe as RADAR Power, ie: my knuckles hit the radar screen. I then call for flaps to approach and gear up at positive rate, I then call for the FO to set max thrust. A story I like to relate is a commuter crew pushed 115% power on a go around with a tail wind and when maintenance questioned the pilot to why he went to 115%, the Capt. said :Because that's all I could get"!!! He gets my vote!

We all remember the Air Florida crash ... if only the pilots would have pushed the power levers to the max position the accident would never have happened. There is no sense in babying the engines in an emergency, because no one is going to a crash site and pick out the engines to be reused because the pilot didn't exceed any limitations.

[MikeD]

Engines are never set to idle during the approach phase, speed is controlled via the speed brakes in landing configuration with minor power corrections. Go around is full mil power and climb, speed brakes in, gear, flaps.

[A300Capt]

GA's normally aren't such drastic maneuvers requiring max thrust and wild pitch attitudes.

In the B75/76, we would select the GA thumb switch on the thrust levers and the auto-throttles would only give you about half of available thrust (no sense scaring the passengers). This would produce about a 2000fpm climb rate which is plenty for most GA's. Obviously, and before anyone asks, the pilots could "manually" push the power up to max at anytime. Btw, the closer you are to the ground the more rapid the auto-throttle response.

The A300's auto-throttles give max power and you're literally pushing forward and trimming forward just to keep the pitch attitude under control. Pitch attitude can be as high as 21 degrees but 17 degrees is more the norm. I personally think max power on a normal GA is a little much and I wish Airbus had toned it down a little.

As far as the approach question goes. 90% is way too high a power setting. Newer jet engines have various "idle" speeds. When you lower the flaps the engines increase from a flight idle speed to an approach idle speed. This gives a quicker response time to "spool up" in the event of a GA. The N1 speed is in the ballpark of 35-40% of max when stabilized on the ILS with gear/flaps down. N2 is probably around 80-85%. Sounds like somebody must have given you N2 figures.

[C650CPT]

[ QUOTE ]
GA's normally aren't such drastic maneuvers requiring max thrust and wild pitch attitudes.

[/ QUOTE ]

I agree that most GA's, especially a planned one deserves smooth control, but I was thinking emergency situations. I think of the one time I did a GA in which I mashed the power levers up ... I had briefed the new FO that the wx might not allow a landing out of an ILS and was prepared to do the MAP, but at DH we saw the lights and continued the approach, at about 100' or less we settled into a fog bank and I lost all visual cues to continue the approach, so I got out of there.

[Visceral]

In the mighty KC-135R tanker, it was:
Pickle(flight director go-around cues), Power, Flaps, Gear, Flaps

[I_Money]

The only time I have about 90% power on landing was on the carriers as they do not have the luxury of time there. If they miss, and do not have the power already there, they swim (infront of the boat - not fun).

[fr8dog]

Try 90% power landing the lear.... I got to get my fellow co-workers to try it !!

[alphaspeed]

One quick note. 90% rotation does not always relate to 90% power. Of course, even taking this into consideration, 90% (rotation or thrust) is way too much for approach.

alphaspeed

[say_speed]

[ QUOTE ]
I agree that most GA's, especially a planned one deserves smooth control, but I was thinking emergency situations. I think of the one time I did a GA in which I mashed the power levers up ... I had briefed the new FO that the wx might not allow a landing out of an ILS and was prepared to do the MAP, but at DH we saw the lights and continued the approach, at about 100' or less we settled into a fog bank and I lost all visual cues to continue the approach, so I got out of there.

[/ QUOTE ]

I think you might be confusing a few people here when you associate a go around with an emergency... A go-around is a normal maneuver, whether you execute it at 20 feet or 200 feet above the ground, the procedure is the same. And the procedure usually calls for max power, respecting engines limitations of course; in an emergency, let's say a windshear recovery, you want all the fresh air the fans can give you.
Pitch and power comes more or less at the same time, but you want initiate the pitch first, and then clean up the airplane.
On a jet, a go-around is not an easy maneuver, when you have 2 engines, (all the engines...) you can satellite yourself quite fast!
Always exciting though...

[Jason]

Actually I would tend to call it an 'abnormal manuever' - not an emergency but no where near what I would call a normal manuever and here's why I say that - that old syaing about 'Plan for a go around hope for a landing' - welll....it just don't work that way in professional flying. Everytime I start down hill I plan to land. Period. A go around is (usually) always an option but in 4,000 hours of professional flying I've executed 4 go arounds - well 8 if you count missed approaches.


Jason

[say_speed]

Yep,
I see your point... Nonetheless, whether you plan for a landing or a go-around, I would personnaly classify a go-around as a normal procedure. I was more talking about abnormal and emergency procedures, as you can find them in your POH or company manuals, like recovery from stall, starting an engine in the air using the APU (abnormal flight ops), or landing with an engine failure, loss of cabin pressure (emergency ops).
It is not because you have done 4 go-around in 4000 hours, that it is an abnormal procedure.
Me, in 1 flight, I have done 3 go-around before I could land the bastard! And I do an average of 4 go-arounds per year... I guess I am just a flying goofball !!!

[smokey1]

I don't fly jets so I was wondering if someone could tell me what N1 and N2 mean and do

[Minuteman]

N1 and N2 are the turbojet-equivalent of piston engine RPM. Its the speed of a rotor in the engine, expressed as a precentage of a maximum speed and is used to determine thrust settings in some engines.

There are usually two or three independently-spinning rotors (shaft that the blades are attached to) in a turbofan.

Took that one, hook, line, and zinker!

[C650CPT]

When you loose sight ( re enter IMC ) of the runway enviroment descending below DH in unfamiliar territory, it is akin to an emergency procedure in the fact that you need to act positively and immediately.

[Ophir]

I will try and explain it smokey but I am only taking a class on it. But it seems that sometimes the less you are directly involved in something the better you can explain it. I guess that comes from being the student and regurgitating well written information.


In a jet engine, or turbojet, there are a series of blades that all compress air into a smaller and smaller area increasing pressure in preperation for the combustion chamber. These blades are all attached to shafts that run the length of the engine. The first set of blades that are visible if you look inside an engine are attached to the N1 shaft. This is also the considered the low pressure compressor shaft. It is low pressure because it is taking air from outside and compressing it. The further you go along the chain events in a jet engine the higher the pressure gets until you reach the combustion chamber where things are exploding and exiting out the back.

Before the compressed air from the N1 shaft makes to the combustion chamber it gets compressed again by the N2 shaft which has the high pressure compression blades attached to it (sometime centrifugal). So air goes from N1 to N2 but each shaft is spinning at different RPMs so as to alter combustion/thrust. The N1 shaft typically rests inside the N2 shaft, or is sleeved by the N2. Both shafts have blades for the exhaust gases to push thus creating the spinning of the shaft. The spinning created from the exhaust gases is attached to the blades on the front of the engine and they are creating compression.

Again this is rudimentary turbojet anatomy of gas generator or core turbine, but I am not claiming to know much. Maybe this will spark further discussion with better explainations.

[say_speed]

[ QUOTE ]
The first set of blades that are visible if you look inside an engine are attached to the N1 shaft.

[/ QUOTE ]


And whether you are looking inside the engine from the front or the back, you are looking at N1...