Yer average domestic flight (over the US), in yer average “workhorse” aircraft (say, a Boeing 737) is flying a regular route (say, STL - MCO), at yer average domestic cruising altitude (which IIRC is 32K feet). Assume no weather, air traffic control, or other complications. It is as mundane a flight as can be.
About how far out from the destination airport does the craft begin its descent from 32K feet (and how does that translate into time-- e.g., 20 minutes from landing? 10 minutes from landing?)?
Also, is there a website that will show me routine flight patterns? I know the plane doesn’t take off heading generally southeast from STL and stay at that bearing until it hits the runway at MCO–obviously there are turns involved. I’m curious about what those turns look like (specifically WRT the approach) on regular passenger routes.
NOTE: I ask these questions solely because I am an aviation buff and would like to learn more about the process.
It all depends on how fast you want to descend and how fast you’re moving. Either way, the standard descend angle is 3 degrees. That is, the slope of the “hill” the aircraft comes down is three degrees.
For approaching an airport, pilots follow a Standard Terminal Arrival Route, or STAR. They’re routes based off of navigational equipment on the ground.
As for the en-route portion of the flight, there aren’t really turns involved. These days, the plane just follows a GPS route that goes straight there.
I think that would depend on the distance between the two airports. If the distance is very long I would assume a pilot would follow a great circle. Also if there is restricted air space between the two points the pilot would have to go around.
Frequent flier here. Decent starts roughly 30 minutes before arrival. Sometimes a little less, occasionally a bit longer.
As far as turns goes it depends on where you are arriving from. For example LAX, if you are approaching from the East the decent starts over the mountains out by Lake Arrowhead and is straight in. From the North the planes will fly down the Central Valley, hang a right south of Bakersfield turn left just off the coast, turn left again over Santa Monica, and hang a u turn over downtown or just east of there to line up on the North runway.
A good website for following detailed flight paths is www.flightaware.com. You can select any specific airport to track the details of local movements in real time. Tracking doesn’t go all the way to the ground, and it doesn’t start immediately at takeoff, since the data comes from approach and departure control and not local tower control. Or you can follow any particular flight or even aircraft type if you wish, including private aircraft but not military ones.
Some of the complexity you’ve probably noticed in local flight paths is the result of noise abatement procedures, which are unique to each affected airport. You can find detailed charts (never mind the jargon, the pictures are clear) for the airport you’re interested in at www.airnav.com or www.fltplan.com.
I’m not a pilot but my understanding is divide your altitude by 300, so for FL320 about 106 nm out. Time to landing depends on speed, which is determined altitude or ATC.
For example below 10,000 ft. the max speed is 250kts. Between 10,000 ft. and FL280 it would usually be around 280kts, and above FL280 it’d be some fraction of Mach. Like .72 for example.
I am not an airliner pilot, but if I recall correctly, 500 feet per minute or thereabouts is considered a pretty standard rate of descent. So, from 30,000 feet about 15 minutes to make the descent.
In an emergency, something like a B737 can safely descend a lot faster than that, but that’s strictly for emergencies, not for routine flights.
However, it’s not just actual vertical descent that a pilot is concerned with. There are pre-descent checklists, standardized approaches for big airports, ATC to communicate with, other traffic to consider… hence, the entire descent process often takes 20-30 minutes and the rate of descent/horizontal speed may not be constant. We do have some airline/big iron pilots on the Dope, I expect they’ll check in shortly.
More or less, although once you get to Class A airspace (essentially, what you’d have above FL280 although the exact altitude varies somewhat) there is, in fact, no speed limit. In Class A the limit is what your aircraft can do and how much of that capability you desire to use.
Well, OK, the FAA does frown on trans-sonic speed over inhabited areas because the people below don’t like getting their windows rattled, but aside from that, you can go as fast as you’re able. Commercial airliners, in fact, don’t fly at their maximum speed, they fly at the most efficient speed for the planned trip to control fuel costs, at that most efficient speed is less than maximum speed.
Well, there’s also the fact most of them can’t exceed Mach 1 in level flight due to not having enough engine power anyhow.
In the US if one feels a need to fly at supersonic speeds one can apply for a waiver. The FAA has been known to grant them though they generally limit such things to above desolate areas. Also, in the event of an emergency one could get away with breaking such a rule if the speed was either required to extract oneself from an emergency, or unintentional (such as from an unanticipated dive).
The short answer is about 100 nautical miles from the destination and it takes about 20-25 minutes from landing and 25-30 minutes from stopping at the aerobridge.
The long answer is it depends on lots of factors. The ideal descent has you pulling the power back to idle* at 32000’ or whatever height you were cruising at, and essentially gliding all the way down until in the last 10 miles and 3000’ where you start configuring the aircraft with flaps out and gear down. Once stabilised at the approach speed the power comes back up to maintain that speed. That’s the ideal but it often doesn’t work out that way, either because height restrictions on the arrival route just don’t allow it or because you didn’t quite work out the descent distance correctly.
There are a few factors to consider when planning the descent.
The ground distance travelled is affected by tail and headwinds so you have to make an allowance for that. If you have 100 knots of tailwind you need to start your descent earlier and vice versa for a headwind.
A light aircraft won’t glide as far as a heavy aircraft (given the same aircraft type and using the same descent speeds), so if you are particularly light you might need to take some distance off your top of descent point (TOD).
Finally the cabin is pressurised to somewhere between 6000 and 8000 feet while the aeroplane is actually flying in the mid 30s. The pressurisation controller will descend the cabin to the landing altitude while the aircraft is descending, but if you descend the aircraft too fast you are in danger of “catching the cabin” which is where the cabin altitude equals the aircraft altitude. If this happens, the passengers stop experiencing the comfortable 325 foot per minute rate of descent the cabin was doing and start experiencing the 1500-2000 foot per minute rate of descent the aircraft is doing. That can be quite uncomfortable for your sinuses and ears. Some pressurisation controllers allow you to manually set a rate of descent. If that is the case you can adjust the cabin rate of descent up to say 500 fpm if it looks like you are in danger of catching it. Other controllers don’t have that flexibility though and in one version of the type I fly (BAe146/Avro RJ) you need to keep the aircraft descent rate to 1000 fpm until you are through 28000’. This avoids catching the cabin. It also requires adding a few miles to your descent point because you aren’t descending as steeply as you normally would.
The rule of thumb for a descent point, as recommended by the manufacturer of the 146, is 3 x your height in thousands of feet equals descent point in nautical miles. This gives a similar answer as dividing by 300 as mentioned by split p&j. For descent from 32000 you would use 96 Nm as a descent point. You should then add 5 Nm for every 20 knots of tailwind or subtract 5 Nm for every 20 knots of headwind. You can then make a further allowance for having a light aircraft if necessary.
That is just a guide and you have to monitor the descent profile as you go down and either add power if you’re getting low on profile or add drag or speed if you are getting high. Adding speed gives you a steeper descent, but often you are close to the max speed already and might not have much to play with. Adding drag is frowned upon because it makes the cabin rumble and the more nervous passengers anxious.
FlightAware is a good one.
Here is a standard route from Adelaide to Melbourne. Ideally it would be a slightly curved line following a great circle track between the two airports. That would be shortest, most direct route. The airways are often arranged like a highway though with aircraft in one direction all following one route, and aircraft going the other way following another route laterally separated from the first. Aircraft going from Melbourne to Adelaide follow another route to the south of the one in this picture. These routes would always be flown between these two cities. The only reason you’d deviate from the published route is if ATC told you to or if you needed to avoid some weather.
At the end of the route, approaching Melbourne, is a STAR, a standard arrival that transitions you from the enroute phase of flight to the approach. Without the STAR the route would terminate overhead the airport on a direct track from ARBEY. The STAR consists of waypoints BUNKY, BOL, PAULA, and EPP. EPP is the start of the ILS approach for runway 27. If a different runway was in use, they’d give you a different STAR. The STAR is entered into the flightplan about 150 miles out from Melbourne, this is when ATC tell you what STAR, runway, and approach they want you to use.
The STAR takes you around noise sensitive areas and keeps you separated from aircraft arriving from other cities as well as departure traffic.
This particular STAR has a height restriction of 9000’ or below by BUNKY. This screws up the descent profile a bit because left to our own devices we would want to be a lot higher at BUNKY.
There are 39 track miles between BUNKY and runway 27 following the STAR. The three times height rule of thumb used before to get our descent point is useful for that purpose but as you get closer to the ground it is easier to follow your profile by multiplying miles to go by three. This gives a slightly shallower profile to three times height but they are similar enough.
Using this new rule, we want to be about 11000’ feet at BUNKY (3 x 40 miles = 12000 feet, minus a bit so we can slow down later on, the decimal point moves as necessary to give the correct number of zeroes). So we want 11000’ at BUNKY but the STAR says we must be at 9000’ or lower, so the STAR puts us low on profile and the last 30 miles until commencing the ILS is flown with a high power setting that gives us a lower rate of descent so we can still fly a constant descent to landing. We might plan to fly the short leg between PAULA and EPP level at 2500’, this makes it easier to slow down for the approach, and it is easier and safer to intercept an ILS approach from below the glide-slope rather than above.
500 fpm would be 60 minutes from 30000, but the descent rate used is much higher, more like 1500-2000 fpm.
First, rules are similar around the world but there are variations, the following is true for Australian airspace. Speeds are generally unrestricted above 10000’ and maximum 250 knots indicated air speed below. At high altitudes there is a huge difference between the speed on your airspeed indicator (IAS), and the actual true airspeed (TAS) you are flying. Speed restrictions are always indicated airspeed while the aircraft will actually be flying faster than indicated. As an example if we have an indicated airspeed of 270 knots at 30000 feet, that is close to 420 knots true airspeed. At sea level though, the indicated airspeed is within a knot or two of the true airspeed.
Our normal descent profile has us descending at 280 knots IAS to 10000’ then 250 knots IAS till the start of the approach where speed is progressively reduced to about 120 knots IAS for the final 1000 feet or so. 280 knots at 30000’ is about 430 knots TAS but by 10000’ we are still doing 280 knots indicated on the airspeed indicator, but the true airspeed has slowed right down to a bit over 300 knots. So for the whole descent we are slowing down significantly as we get down into more dense air even though the airspeed indicator says we are doing the same 280 knots.
*“Idle” being the minimum engine power setting for the conditions. Pressurisation and anti-ice protection uses air from the engine compressor stage and the flight idle power setting has to be high enough to supply those services. At high altitudes with high demands from the services there is still significant residual engine thrust.
Not to be snarky, but if you’re an aviation buff, you’d easily know initial descent typically starts at 30 minutes out. I fly frequently, and this is the norm.
Aviation buffs come in different flavors. Someone an expert on WWII warbirds won’t necessarily by knowledgeable about modern airliners. Someone who is expert on modern Boeings in the 7x7 series may or may not know jack about small single engine Cessnas.
Sorry about that - I probably confused cabin pressure descent with actual descent, but then, I’m not an expert on those sorts of airplanes. Thanks for the correction.
A related Q: is a great circle route actually curved “on the ground”? I find it hard to get my head around this. I know they look curved on a map, but if you’re flying a great circle route are you constantly turning in reality? If so, do they simplify these routes to a series of straight lines that approximate a great circle?
No, they’re not curved on the ground, but they ARE different than a line of constant compass bearing. It’s only because planes happen to use compass bearings (true or magnetic? I’m not sure) to navigate, that they therefore have to make adjustments mid-flight to approximate a great circle route.
P.S. Great circle routes don’t look curved on ALL maps. Check out a polar projection, e.g.
Lordy, I have lost count of the number of times I have done that one. The thing that always strikes me is that the plane hardly seems to get time to actually level out before it is descending again. I remember Amsterdam to LHR in a 777, and I’m sure that didn’t get to cruise.
I was just following a few links and found this:landing in Butan. As far as approaches go, this must be right up there.
You are not turning all the time, the ground is already curved for you. (It is a straight line, essentially by definition.) As pointed out above, your angle with respect to the Earth’s poles (either true or magnetic) does change (except for the special case of flying around the equator), so if you have a map projection that preserves angles relative to the pole (ie Mercator) the path on that map is a curve. A straight line on a Mercator projection traces a Rhumb line - a line that has constant bearing. Which is what you tend to use if all you have is a compass, and is probably the main advantage of such projections. Long distances tended to be made up of a set of rhumb lines that fit close to a great circle. GPS and other nav aids make that a thing of the past for most modes of transport.
This is one reason why I believe everyone should own a globe of the Earth. Flat maps distort our perception of reality too much. Spatial and geo-political perceptions for a start.
Amen to that. Owning a globe is ideal, but playing around with Google Earth at small scales (high altitudes) isn’t a bad substitute.
So…most big planes these days use GPS in the sense that the computer keeps track of current location by GPS, knows the GPS location of the next waypoint, and makes adjustments (when on autopilot) to the steering mechanisms to keep on a “straight” path to that waypoint.
HOWEVER, it’s just as easy to program the computer to calculate this as: 1. A truly straight great circle line, or 2. As a single compass bearing – a rhumb line – that will necessitate tiny, constant, unnoticed-by-the-pilot adjustments en route from a truly straight line.
BECAUSE the aeronautical charts and flyways were developed during the era of compass navigation, I assume that what really goes on is #2. This must be so – pilots still say they are on a bearing of 270 or whatever.
(It is a straight line, essentially by definition.) As pointed out above, your angle with respect to the Earth’s poles (either true or magnetic) does change (except for the special case of flying around the equator), so if you have a map projection that preserves angles relative to the pole (ie Mercator) the path on that map is a curve. A straight line on a Mercator projection traces a Rhumb line - a line that has constant bearing. Which is what you tend to use if all you have is a compass, and is probably the main advantage of such projections. Long distances tended to be made up of a set of rhumb lines that fit close to a great circle. GPS and other nav aids make that a thing of the past for most modes of transport.