Eddie Sez:

If you have a heads up display and/or synthetic vision, the flight path vector is your best friend. What follows are some explanations on how we do the following tasks without the flight path vector and how we can do things better with it:

Before we do that, however, let's get some terminology straight. . .


HUD Geography

Flight Path Vector

The flight path vector shows where the airplane is headed. On the HUD, it shows the pilot the airplane's vector in relation to all the weather, to the runway's database position, and to terrain as infrared characteristics permit. With synthetic vision, it will shown the airplane's vector in relation to the terrain and the runway's database position. With just a few exceptions, your primary focus is on the flight path vector.

Bore Sight

The bore sight is the nose of the aircraft, which is where the airplane is headed adjusted for Deck Angle, and drift. It is where the pointy end of the aircraft symbol appears on a conventional attitude indicator. You will need to focus exclusively on this in the event of a wind shear recovery maneuver; the flight path vector will be greatly impacted by the wind and aircraft performance during the recovery. During a CFIT escape maneuver you will also focus on the boresight, but the flight path vector will be of use on you synthetic vision. (More on that below.)

Reference Flight Path Angle (FPA)

The reference flight path angle (FPA) draws a line at a selected angle from the airplane to the ground or the air above. It is independent of aircraft attitude.



Weather Avoidance

Will I clear it?

Using a pen and a steady hand you can come up with a guess. Of course this takes time and your head position is a factor.

With two one-dollar bills you can increase your accuracy. See 2 Dollar Technique for how to do this.

Of course the flight path vector makes all this easy.


Terrain Avoidance

Movement on windscreen

You cannot judge terrain clearance by the position of the terrain on your windscreen in many cockpits; the parallax caused by the thickness of the glass may distort that view. The only real judge is how that terrain moves on the windscreen: if it is moving down you will clear that point provided aircraft performance doesn't decrease. But remember aircraft performance probably will decrease with increased altitude.

Flight path vector on synthetic vision

If you are performing an honest to goodness PULL UP response to a GPWS warning on rising terrain, by all means perform the AFM maneuver, such as the G-450 CFIT escape maneuver. But if you have synthetic vision it really pays to have the flight path vector up, especially when IMC.

Remember to perform the maneuver while looking at the aircraft boresight, that shows where the nose is and gives you the best idea about how to max-perform the aircraft's vertical escape. But try to take a look at the flight path vector while you are at it. It will tell you if you are going to clear the terrain or not, but it also gives you a view several degrees left or right. Maybe you can make life a lot easier, and livable, by sneaking in a few degrees of bank one way or another.


Runway Lateral Alignment

You want to have everything lined up before you get to Stabilized Approach Height and the easiest way to do that is with a good, straight-in instrument approach. But what if you don't have that?

Imaginary rope

Getting a T-37 lined up with a small runway was never a big deal. Flying the Boeing 707 into a small runway always was. To help us with that task we came up with a few gimmicks, some just mind games, some mathematical.

Lateral alignment seemed to be problematic for some. You couldn’t turn the big Boeing on a dime and getting the airplane lined up took some practice. The drawing comes from my original notes back in Hawaii.

It seems silly, after all these years, but this is what we taught and I suppose this was supposed to help. But it is all we had to go with.

“Imagine a rope,” I would tell the younger pilot, “hanging from a pole on the far end of the runway. . .”

Sometimes the imagery would help, sometimes not.

Extended centerline on synthetic vision

With synthetic vision, the runway is drawn on the display with lead in lines complete with index marks. Lateral alignment is simply a matter of flying the airplane over the line.


Runway Glide Path Interception

Vertical alignment can be even trickier than lateral. Judging your angle to the runway is problematic because each runway appears different. The length of the runway versus its width can fool your eyes. The surrounding terrain can make you feel high when you are in fact low.

Having an ILS or LPV glide path is a great check for vertical alignment but if you don't have that, you should have a back up.

Visual perspective

One of the misconceptions about flying airplanes in general and landing in specific is the role of depth perception. Nobody has depth perception at night, and yet some pilots have their best landings at night. The brain tends to process angles subconsciously and derives height information from these angles.

Our notes in the Boeing squadron used these angles, while not speaking of them as items of math, they did mention that perspective is what is important when judging vertical alignment:

DME countdown

Using the 60 to 1 concept, you know that a three degree glide path should keep you 300 feet in the air for every nautical mile from the runway. At 2 nm you should be at 600', 3 nm at 900', and so on. If there is a VOR near the runway, you can figure the DME at the touchdown zone and subtract that. In the example drawing, for example, the VOR is a mile from the end of the runway.

Your FMS should also have the runway end programmed, giving you another excellent countdown of the miles to go. Just multiply the miles to go by 300'.

Reference Flight Path Angle (FPA) Line and flight path vector

The HUD draws a line from the airplane to the ground at whatever angle you command. This angle comes from the airplane to the ground. The line it draws on the ground shows where your airplane will end up if you follow that angle.

Understanding that the line comes from the aircraft and not the ground is vital to using the line to your advantage. In each of the three examples, the flight path vector is right on the touchdown zone of the runway.

If the line is short of the runway, you need to “walk the line up” by reducing your angle of descent. In the drawing you have raised your pitch to the touchdown zone but your flight path angle is still short of the runway. This means you will indeed land in the touchdown zone, but at too shallow an angle. You should further reduce your angle to "return to glide path."

If the line is beyond the touchdown zone of the runway, you need to “walk the line back” by increasing your angle of descent. In the drawing you have decreased your pitch so that the flight path vector is on the touchdown zone. This means you will land in the touchdown zone, but at too steep an angle. If time permits and you are above Stabilized Approach height, you should further increase your descent angle to "return to glide path."

If the line is on top of the touchdown zone of the runway, that is where you will end up if you don't flare. A proper flare consumes less than 500'.


Runway Aim point

Stationary point on windscreen

It works in a Cessna 150 and it works in a Boeing 747: the airplane is heading for the spot on the runway that doesn't move on your windscreen. Of course that is a lot harder to judge at 150 knots versus 50 knots.

Flight path vector on runway touchdown zone

With a flight path vector and HUD all the guessing is history; simply place the flight path vector on the touchdown zone and keep it there until it is time to flare.

Video: Flight Path Vector (HUD) KPSM Runway 34.


References

Davies, D. P., Handling the Big Jets, Civil Aviation Authority, Kingsway, London, 1985.

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.