Jump Run uisng a Garmin 430

Here's how to use the Garmin GPS system to plan your skydiving jump run. This guidance continues the Spotting Brief and aims to train pilots at Bridlington DZ (UK). Remember that usage and requirements can vary by DZ or country, so always adhere to your local guidelines.

The Garmin 430 GPS has been a staple in skydiving operations for over two decades. However, with technological advancements, Garmin has announced the 430 will be phased out by 2024. The good news is that the new GTN series retains all the necessary features for skydiving, albeit with a few changes, including a touchscreen interface. This might be a bit tricky for those accustomed to wearing flying gloves. For the purpose of this blog, I've replicated the interface of the 430 unit. It's not an exact match in appearance and scale, but it's close enough for our purposes and simplifies the process of adjusting numbers and headings.

The 430 and GTN models let you customise the graphical interface to include your preferred map layouts and navigational features. In this guide, I'll display the unit using a North Up map orientation, complete with readouts for bearing (BRG), cross-track error (XTK), distance (DIS), and ground speed (GS). The map view is set to cover a 3.5-nautical-mile square, and you'll notice a green circle with a diameter of three nautical miles, which is my layout of choice.

For comprehensive guidance on GPS setup, consult the Garmin 430 manual, which can be found https://static.garmin.com/pumac/GNS430_PilotsGuide.pdf, or search for an alternative source if the manual is no longer available.

Here's a quick summary of the startup process:

1. Power up the unit and wait for its internal diagnostic checks to complete.

2. Press the OK button twice to navigate to the "searching for satellite" screen.

3. To find the DZ (Drop Zone) reference, press the "Direct to" button and scroll through the letters using the large and small wheel of the righthand control until you have the name BRIDDZ.

A shortcut for step 3 is to scroll to the bottom of the navigation page, where you'll usually find the last selected destination. A video illustrating this method is available here.

https://www.youtube.com/watch?v=2HvddEH0EFg

Note: Aircraft at drop zones mostly fly in circles, so GPS units are often not updated with the latest maps and airspace information. These devices should not be relied upon for cross-country flights. Always have an up-to-date, recognised navigational chart on hand, either in paper form or as a moving map.

Setting our running in direction

Pressing the OBS (Omni-Bearing Selector) button will enable you to enter the run in the direction you require. The example below is 030—you need to wait until the unit has a satellite fix, or it just gets messed up. If the Garmin has been slaved with a Garmin or Aspen digital instrumention, then you will be able to set the OBS direction from those units.

The magenta line will stretch from the downwind area to your specified "Go-to" destination, which in this case, is the centre of the PLA. Conversely, the white line extends from the destination into the upwind zone. Your route should follow the magenta line, transitioning into the jump run typically along the white line.

Planning the route to the exit point and height

Using the Vertical Speed Indicator (VSI) and the GPS, we can determine our route to intercept the exit point at the correct altitude. This calculation is a rule-of-thumb estimate. For example, flying at an Indicated Air Speed (IAS) of 80 knots translates to travelling approximately 1.33 nautical miles per minute since 80 knots divided by 60 minutes equals about 1.33. However, this calculation does not consider factors like climbing at 80 knots, which affects the slant range and results in a reduced ground speed, nor does it account for wind effects.

For simplicity, let's assume that climbing at 80 knots IAS gives us an average of 1.2 nautical miles per minute. At 100 knots IAS, the travel rate is about 1.66 nautical miles per minute; we can approximate this to 1.5 nautical miles for easier calculations, disregarding headwinds and tailwinds as part of this rule of thumb.

The VSI indicates a climb rate, which for a climb at 80 knots could be around 500 feet per minute above 7,000 feet for a piston aircraft, simplifying the calculations. With these basic figures, we can approximate the track miles needed to reach our intended altitude and location over the ground.

From 7000ft, climbing at 500ft per minute will take 6 minutes to reach 10,000ft. Multiplying 6 minutes by 1.2 nautical miles per minute results in a required track mileage of 7.2nm (6 x 1.2 = 7.2). This is a rough calculation that should be tested during the climb. For example, flying 3.6 miles away from the drop zone (DZ) only to find the estimate incorrect when we turn back could result in the flight taking longer than desired.

When a waypoint is added to the Garmin 430 and set as an airfield, it will display a green circle with a diameter of 3nm around it. This can serve as a visual guide for flying the track mileage. Note: The dotted yellow line and distance markers are unavailable on the Garmin. They are shown here purely for explanation purposes. A picture is worth a thousand words, after all.

In the image above, there is no wind as indicated by an Indicated Air Speed (IAS) of 80kts, True Air Speed (TAS) of 91.2kts, and the Garmin shows a ground speed of 91.2kts. As we pass over the edge of the green circle, take a mental note of the altitude and the VSI climb rate. As you pass over the middle of the Planned Landing Area (PLA), see if the aircraft has climbed just over 500ft. You can continue testing by flying to the far edge and further testing with 1.5nm crosswind legs. By staying close to the PLA, we can adjust our path at any time if we find we are climbing faster or slower than anticipated. A strong headwind could result in climbing 500ft in less than a mile, and it might take over two miles when climbing downwind.

Warning: If you are flying at a DZ with multiple aircraft operating, you should avoid entering the green circle until it is your turn to run in.

Continually climbing, in a turn, is inefficient, so however you test the maths on the track mileage, try to keep the wings level during the climb as much as possible. However, avoid flying too far away. It’s definitely a compromise.

Thankfully, with time, you will begin to learn the performance of the aircraft you are flying and will start to know the required track mileage without having to perform these calculations. But for now, we have to teach something more than just using intuition!

Jump Run

Drawing from our initial example in the spotting brief (link), the jump run is set at 030 degrees, and the exit point is located at -0.1 (or 0.1 nautical miles before the centre of the PLA).

Jump Run: 030

Exit: -0.1

Separation: 9s

Abbreviated spotting Recap

From the 214 data, our initial focus lies on wind direction within the 1,000 to 5,000 feet range, encompassing the parachute deployment heights. We observe variable directions between 020 and 040 degrees when assessing wind direction. Taking the mean, we opt for a run-in direction of 030 degrees. In terms of wind speed, averaging between 1,000 and 2,000 feet yields 15 knots in this instance, which gave us an exit point and direction of 030 -0.1

The display above shows the aircraft is 1.5 nm downwind from the centre of the Planned Landing Area (PLA), with the bearing aligned to our selected course. The cross-track reading indicates that we're just 0.02 nautical miles (approximately 120 feet) to the right of the line. Let's set a challenge for ourselves, the "Cross-track Challenge": Your goal is to never stray more than +/-0.10 nm from the designated wind line (either the magenta or white line) during the entire jump run. This translates to a deviation of no more than 600 feet (or roughly 185 meters) on either side of the jump run path.

Calculating the Engine Cut and Exit

The distance to overhead is 1.5nm, and as we want to start the exit at -0.1nm, this means we have 1.4nm left to run. Our ground speed is 80.0 knots. Our indicated airspeed is also 80 knots, typical for a piston aircraft, which gives us a true airspeed of approximately 96 knots by rule of thumb. The winds aloft are reported as 030 at 15 knots. Depending on your location, you would typically relay this information to the ground and jumpmaster as either:

- 16 knots headwind

- Ground speed is 80 knots

- 9s separation

For Bridlington, we report the wind on the nose.

With experience, you will start to know how long it takes to configure the aircraft for the jump run, including engine settings and flaps (if required). Typically, I begin configuring the aircraft about 30 seconds before the exit. With little to no wind on the nose, this might be adjusted to 0.5nm before the exit. This will be covered in more detail during the hands-on training; for now, appreciate that the faster we travel over the ground, the sooner we need to start configuring the aircraft.

Note: We can only report on the conditions we observe and in a manner preferred by DZ control and the jump master. How that information is used to plan the exit strategy and the conditions below the aircraft is out of our hands (UK rules).

Wingsuit deep spot

In the spotting brief, I talked about the Wingsuit large groups, or flocks as they are known, requiring a perpendicular spot several miles upwind.

The Garmin 430 is still a good choice for this type of run-in, although we refer to it slightly differently. Note: the picture below shows a yellow dotted line and white protruding from the aircraft. These are not available on the unit and are just there for reference.

Using the green circle as a visual guide, we can estimate the 3-mile mark for our jump, represented by the yellow dotted line. By adjusting our heading to compensate for the crosswind, we follow a perpendicular track based on the distance indicated (DIS). The distance is measured from the centre of the Planned Landing Area (PLA), our target destination. We are looking to cross the jump run white line at 3 nm, so we need to be slightly further out than 3nm. We now use the cross-track (XTK) as our distance from our target spot.

Once we have XTK of 0.30nm, and the white line is behind us, we can turn on the green light, and with the heading and track dialled in, we will see the distance (DIS) gently rising due to slant measurement.

As with any training, having a general overview can significantly ease the information overload experienced during hands-on flying. It might seem complicated at first, but in reality, flying involves mastering many small tasks. These tasks aren't particularly difficult on their own; the challenge lies in managing all of them simultaneously within a short period of time. With practice, what initially appears complex will soon become second nature.