Well, you're up there, now you need to get down -- gracefully.

In this class you will learn about:

• Planning your descent
  
  
• A STAR - not the one in the sky
  

Planning your Descent

You might think that a descent is pretty easy, once cleared to descend, you cut the power and point the nose down. The basics are straightforward, but the finesse is to fly it in the most efficient and comfortable way. You need to stay high as long as you can to conserve your fuel, keep your speed up, and to potentially avoid weather. But you can't wait too long to start your descent, otherwise you will end up too high as you approach the airport. Then you will need to make extensive use of speed brakes, which means that you wasted fuel to stay high longer than you should have. You also need to respect the altitude and speed restrictions given to you by ATC.

The old hands will already know the rules to an idle decent, but here is a place to start. You will obviously descend sooner, the higher you are. You will want to maintain about a 3° slope on the way down, that is a 20:1 slope. So you fly 1nm (6000ft) for every 300ft you drop. That is the rate descent that most aircraft are designed for.

Although you may rely on automation, such as VNav or the excellent freeware vasFMC utility, you still need to be able to do the mental arithmetic yourself, to keep tabs on things, and to ensure you are on a safe course. It is often useful to keep in mind the approximate figures of 10nm for 3,000ft descent and 30nm for 10,000ft descent -- you can then quickly "count" along your descent profile.

Top of Descent (TOD)

To start your descent, ATC will assign you an altitude restriction at a waypoint. You may also get a speed restriction, but even if you do not, you will generally find that aiming for a speed of 250knts at altitude restriction points at or within 12,000ft of ground level, will work pretty well to set up your approach.

The descent clearance will generally be given as "at pilot discretion." If so, it is up to you when you start your descent, you just need to meet the conditions given to you by ATC. Occasionally you will be instructed to start your descent immediately. If you are not certain what you are being asked to do, be sure to ask for clarification.

So the TOD is the key thing to calculate, you have to know when you need to start your descent. The basics for this are fairly simple, but the nuances can be complex. There may actually be multiple TODs to keep in mind. For example, ATC may have you descend initially to say FL240, well in advance of your original calculated TOD. You will now be flying at FL240 for a while, and you will need to recalculate a second TOD at that lower altitude to guide you for your next descent segment.

To calculate a TOD, start by taking your cruise Flight Level and subtract the elevation that you need to descend to. That may be the airport elevation, or an intermediate altitude restriction that ATC has given you.

Then, give yourself three times the difference divided by ten ... (3 * (Flight Level - target altitude in hundreds of feet)/10), plus an extra 10 miles to slow down, like so:

    3 * ((FL - target in 100's)/10) + 10

An example, leaving FL320 descending to 11,000:

     3 * ((320 - 110)/10) + 10 = 73nm

If you are allowed discretion as to when you start your descent, then when at your calculated top of descent point, announce to ATC that you will be leaving flight level 320 (in our example here), set the desired altitude to descend to, idle the thrust, and then trim your pitch to capture a VS of five times your ground speed, this will get you very close to the 3° descent that you want. You will find in a well simulated plane, that your airspeed will be reasonable with these parameters.

If you are using a simple panel, this is one time that you can use a VS descent fairly safely. You would set the VS to 5x your ground speed, and monitor your airspeed to ensure it is safe. For example, if your panel shows that you have a ground speed of 450knts, then you should control for a VS descent of 2250 fpm. But, keep watching this, as if the winds change as you descend, you may need to adjust. This approach technique will correct for the winds aloft for you.

You should descend keeping your speed in Mach relatively constant, and then at FL250 switch to keeping a constant indicated airspeed. At 10,000ft you need to slow to 250knts. Be sure that when you are entering a Terminal airspace, even if you are still above 10,000ft, that you are below 250 knots. In some Terminal airspaces you may be further speed restricted as you descend, the charts will detail this.

Monitor It!

Sometimes thing can go awry, always keep monitoring your descent path. Do the math quickly in your head. Just think 30nm = 10,000ft of descent, easy to count by 30's. When you have to slow, figure 1nm for 10knts speed slowdown, even easier to remember. An approximation, but close enough, and a handy figure to keep in mind towards the end of your approach.

If you think about it, this makes 10 knts of deceleration about equivalent to 300ft of altitude descent, in terms of distance flown. If you are stuck a little higher than you'd like due to ATC, and it is not unreasonble to do so operationally, then consider slowing down the aircraft to "buy" yourself some descent room. 30 knts of deceleration will buy you about 1000ft of descent in terms of distance flown. You will have slowed sooner than you needed to, but it will keep you from being stuck too high and fast later on.


Now, you monitor it not only because other factors may affect your descent, but also because ATC may change your altitude and speed restrictions, depending on traffic. You may have to rejig quickly to adapt.

There are other extraneous factors that may throw your descent off, but these are more advanced issues. These include the weight of the aircraft (heavier aircraft take longer to start a descent), an altimeter that is well off standard (gives you extra/less altitude to descend through as you cross transition level), the altitude you start from (the higher you are the longer you are affected by other variable factors), but the largest single issue that you will see is the winds.

Orientation

Well, you always need to know where you are, but it becomes especially critical as you approach the ground, nasty things live there, and are waiting to spoil your day.

All UVA flights are IFR, which means that you should have ATC guidance. In the virtual world, this is not always the case. When you are flying without good ATC (VATSIM Live ATC, Radar Contact), then you are on your own to some extent, and have to establish safe terrain avoidance and vectoring to the Initial Approach Fix (IAF) for the instrument approach procedure (IAP). Do not rely on the built in Flight Simulater ATC, it is neither knowledgeable nor safe. If that is all you have available, best to just turn it off.

If you are flying without ATC, you should be very clear on the Minimum Safe Altitude (MSA) for the area, for the runway that you are approaching. We do watch for this on checkrides. Normally MSA is only used as a backup procedure, if ATC or your radio is out, but obviously this can mirror your simulated flight situation.

The MSA is always prominently marked on any IAP chart as a circle graphic with altitudes corresponding to the approach direction. This is usually noted as a safe altitude out to 25nm from a navigation station. Unless ATC vectors you, you may not go below this altitude until you are established on the published instrument approach route, which may not be until you intercept the localizer itself. ATC has lower minimums for certain vectored paths, but as a pilot you do not have direct access to this information.

Shown at right is the MSA graphic for KORD Rwy 4R. For a distance of 25nm from ORD (Chicago-O'hare) VOR you may safely descend down to no lower than 3400ft ASL when approaching from the SE, and down to 2600ft ASL when descending from the other directions. Be sure to set your altimeter for the correct barometeric pressure, so your altimeter is reading correctly. ATC should give you the barometric pressure when you start your descent.

Besides providing safe terrain avoidance, it is very helpful to have a continuous idea of just how far away you are from your destination airport. Any larger airfield will have a mid-field VOR, or maybe several. Note these and tune them. Make sure you are at the right altitude, based on how far away you are, using the rule explained above.

If you are blessed with a FIX page in a complex panel, use it! It lets you draw circles or radials from any two waypoints or an airport on your Navigation Display, and it persists. Superb for spatial orientation, especially in a busy Bravo airspace, or on final approach. At a glance you know you should be close to the OM, or when to drop your speed, or gear or whatever.

As you approach the airfield, you should be about 6000ft above the airfield level (AFE) at 20nm out, and 3000ft AFE at 10nm. If you are way off these rules of thumb, you are going to have difficultly establishing a stable approach, and you know what happens after that! Of course if you are approaching from the opposite direction, you have an extra 10nm to 20nm to descend as you will be looping around to land in the opposite direction. So especially if you are approaching with a more or less straight-in landing, and with tailwinds, be careful, you can easily get stuck with too much energy, and end up too high & fast.

Getting Close

As you get within 20nm of the runway, start planning your slow down from 250knts and for flap extension. Do not slow up or extend flaps before this, unless required by ATC. Always fly 10knts above your flap minimum speed, for safety. For the 747 fly at the minimum speed for the next flap setting up.

UVA SOP for flaps/speed on approach is 1deg on the downwind (optional, more for the bigger Boeings), 5deg/180knts for the base and intercept, 15deg/geardown/160knts on glideslope (GS) alive or 9nm whichever is later, and then 30deg/Vtgt on GS interception, and no later than the Final Approach Fix (FAF).

For the 747 it is a little different, it is 10deg flaps for the intercept, and 20deg on geardown.

For the turboprops and light regional jets, it is 1 click of flaps for the base & intercept (about 8deg), and 1 click short of full flap extension (about 22deg) on geardown.

You will find a discussion of the "Downwind", "Base" & "Final" parts of an approach in the Pattern Practice section. Vtgt (VSpeed - target) is the wind corrected Vref30 speed, just think of it as your "target" speed for the approach. Vtgt and other Vspeeds are fully discussed in the UVA Flight Planner (FPD) docs, and touched on in the next class.

flaps & speed settings	turboprops & regional jets	jets	747
on the downwind	clean	1deg (optional)	1deg
turning base & intercept	8deg/180knts (slower for a turboprop)	5deg/180knts	10deg/180knts
GS alive or 9nm, whichever is later (gear down)	22deg/160knts (slower for a turboprop)	15deg/160knts	20deg/160knts
GS interception, and no later than final approach fix (FAF)	45deg/Vtgt	30deg/Vtgt	30deg/Vtgt

VNav - An Advanced Topic

If you have a complex panel, with a full FMC, and access to accurate winds aloft, then descents are much easier to handle. But, probably most folks starting out do not have this, and indeed in a turboprop you likely will never have this. Nonetheless ...

VNav in the PMDG 747 is very good at calculating descents, but you have to give it all the information it needs. One of the key things missing, if you don't input it, are the winds. If you have Active Sky or another good source for winds aloft, just grab the winds at your destination at 12,000ft, FL240 & 340, and go to the descent page and hit forecast. If you don't have them, just guess at 1/2 the current wind at your cruise level, you won't be too far off. Put those winds in, and you will get a much more accurate descent.

The LDS 767 is a little more quirky with this in my experience, and unfortunately the PMDG 737 NG simulation (although it will accept it) will not use the winds data to change the path.

Unlike its big brothers, the 737 FMS will not intelligently shift from VNAV spd to VNAV path as required, to finesse the descent, it just gives up, you can fly it directly using the MCP or handflying it, recapture the descent, and then reengage VNav.

But here is a trick. If you don't have the winds aloft data or you are using the 737 NG (in particular if the prevailing winds are tailwinds), you may end up high/fast. To get around this, just specify a speed restriction lower than required. For example, approaching San Francisco on MOD3, at CEDES you might normally set 250knts/11,000ft, instead set it at 210knts/11,000ft!

As you get down towards 11,000ft and the speed tick drops to 210 knts, you will find that you now have more room to maneuver. Of course be very careful not to stall!! The alpha floor protection built into the VNAV in the 747 will protect against that -- but at this point you will likely be about to switch to VNav speed intervention mode (or SPD mode if you must), so it's not a problem -- you will be on top of it.


Another trick, in the PMDG 747 & LDS 767, you can also overstate the tailwinds or understate the headwinds to give you some more "room". If you have a headwind aloft of say 60 knts, instead specify a head wind of only 20 knts. This will achieve the same thing.

A Star

A STAR is a Standard Terminal Arrival Route. It is a standardized procedure for aircraft flying IFR, that is published for ATC and pilots, so that the routing approach to a busy airport is more organized and automatic. Everyone knows what to expect beforehand.

Not all airports have STARs, but large ones will have many.

A STAR will begin with at least one, and usually multiple transition points. Think of a transition point as an entry to the procedure, it can be an exit as well. The traffic will then flow down like along branches of a tree "downward" to a central final point, or perhaps several if the STAR serves more than one airport. Once you are at the final point (or often even before that) ATC will vector you to join the IAP (Instrument Approach Procedure) for your runway.

You will usually find suggested airspeed and altitude "restrictions" on the STAR, which gives you a speed/point in space to shoot for as you descend. They may be labeled as "expect ..." in which case ATC will confirm these, but you can usually expect them. They may be labeled "fly ..." in which case once cleared to fly the STAR by ATC, you fly as per the directions, ATC does not then need to further confirm the restrictions to you. The charts will be filled with other useful information that will help guide your approach.

Traditional STARs you could fly entirely by VOR navigation. For even greater routing flexibility, newer STARs often rely on waypoints that are no longer defined along VOR radials, and to fly these you will need inertial guidance (INS/IRS) or GPS systems. These are clearly labeled with (RNAV) in the title.

Now, the companion question is, What is a SID? Well, we looked at one already earlier. A SID is the same as a STAR, but having to do with your departure, that is a Standard Instrument Departure procedure.

When flying checkrides, use of STARs (and SIDs) is mandatory, so you should start navigating them now.

An example STAR

Let us look at an example, this is paraphrased from a forum post.

Let's pick a chart, the BDF5 arrival into Chicago (Bradford 5), you can find a pdf of it here on the myairplane.com site so you can follow along.

A couple of things to note:

1. There are a number of transitions, or entrances, to this approach. Shown with green arrows are VORs IRK (Kirksville), FTZ (Foristell), STL (St. Louis) and intersection BAYLI.
   
   
2. The typical approach on this STAR will have you crossing BDF (Bradford) VOR at FL240 and BENKY intersection at 11,000ft, these waypoints are circled in green.
   

Some notations:

• The altitudes between the listed waypoints are the MINIMUM altitudes for the route, it would be very rare that you would fly that low during the procedure.
  
  
• The numbers in parentheses are the distances between the waypoints.
  
  
• The numbers in the shield-shaped bubbles are the DME distances to the next VOR. For instance, KEOKK is marked with an arrow with 60 in the bubble, meaning that it is 60DME from the IRK VOR. NEWRK is shown with 52 in the bubble meaning it is 52DME from the BDF VOR.
  
  
• The racetracks at LOAMY, BDF, BENKY, etc. are published holding pattern locations. ATC may ask you to hold over these locations.
  
  
• VORs like Quincy (UIN), Capital (CAP) and Pontiac (PNT) are listed so you can crosscheck your progress with your NAV radios. Don't forget to take advantage of that.
  

So, it is like a tree, going from branches, down to the trunk. There is a lot of information in these. BDF5 doesn't have a page two (or three) like many other STARS do, with further explanations, clearance requirements, or lost communication paths.

Jeppesen Clinics

Jeppesen produced some procedure plates "clinics" around MSFS 2002 that are located here. It may take a bit of time to read through these, but the information is encylopedic.