Changes In Altitude and Speed

1fearfulflyer

Lifetime Elite
I was just tracking a flight that I'll be taking next Monday and I noticed that there are occasional changes in altitude, usually 60 or 120 feet, logged during the flight. Obviously, aircraft don't always fly every single second at the exact altitude chosen (due to changes in wind, etc.) and the autopilot corrects it back to that desired altitude.

You can see an example here at 8:44 am and again at 8:51 am:

http://flightaware.com/live/flight/UAL267/history/20120429/1201Z/KEWR/TNCM/tracklog

My question is are these minor changes simply adjustments by the autopilot that are enough to be logged? Are they also indicators of turbulence?

As for speed, are the ripples seen in the graph simply changes in wind direction that cause the speed to increase/decrease? I would imagine once cruising altitude is reached, the engines pretty much stay at the same power unless they need to be adjusted.

While I have issues with feeling like I don't have any control, flying is still truly fascinating to me.
 

B744drvr

Lifetime Elite
Small deviations in altitude may be caused by turbulence, but I can't tell you that for sure as I don't know what exactly their sources are for the flight data. It could also mean there are some discrepancies in the gathered data by Flightaware.
Displayed speed is the Groundspeed and the ripples are indeed the changes in wind direction and force.
 

pinworm

Lifetime Elite
Yes, small bumps can displace the plane a bit, but usually not more than 50 ft. If the crew does not reset altitude bugs (weather changes in airpressure need to be constantly compensated in addition to msl, or the plane "thinks" it is higher or lower than it is..this deviation is usually in the range of 10's to low 100's of feet). Sometimes deviations are deliberate, looking for better air or avoiding an unstable cloud.

The problem with the flightaware speed is that it does not specify if that speed is "airspeed" or "groundspeed". Airspeed is the speed the aircraft is moving through air, and groundspeed is the speed point to point that represents how long it will take to get somewhere, relative to the ground. They usually differ. In a headwind, airspeed increases and groundspeed decreases..so a plane that appears to be going say 400mph in the air may only be moving 325mph relative to the ground. And vice versa..a good tailwind will reduce airspeed relative to groundspeed..many fliers remember that week in 2009 when westbound flights in northeast broke groundspeed records for civil aircraft due to amazing tailwinds. My father and sister were on one and I tracked it at Mach 1 on flight tracker. Of course the A320 did not break the sound barrier, that was groundspeed. Airspeed was normal. And eastbound flights were showing very high airspeeds and stupidly low groundspeeds, making flights VERY long.
 
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