ST3400 TAWS/RMI How Smart Is It?

As a very smart person once said, "Simplicity is a complex undertaking". The ST3400 is a product that is a living testimony to that concept, a hugely complex piece of technology delivered in a simple, easy to use and understand form.

When we designed the ST3400 we started with a simple concept: the ST3400 had to be the highest performance product available at any price, and be equally at-ease in VFR or IFR flying. This “simple” concept turned out to be rather complex to implement.

The Problem

Making a VFR/IFR capable terrain warning system is easy to do in enroute flying but very hard to do when landing. The biggest problem facing the designer is not how to produce a valid alert, but how to suppress an invalid alert. Stated another way, during enroute flying the system logic is relatively simple because since you’re not landing and you can produce an alert by comparing terrain to altitude. But when you’re landing this logic doesn’t work. Why? With the airplane always pointed to the ground, you certainly don’t want false alerts on your way to the ground.

The ST3400 VAP concept of runways. Note that
the Virtual Approach Path is based on the terrain
itself, not an ILS.

You might consider the use of the GPS/FMS flight plan to make a determination of the landing airport. But what do you do when you’re not on a flightplan, or what if you fly off-flightplan for any reason (either to a different runway, circle to land, or just plain continuing VFR?). The system must not act differently in those conditions, either by being less safe or by producing nuisance alerts.

So, how do you make the system smart about understanding the pilot’s intentions based on the position and path of the aircraft in relation to the runways?

VAP’s and Runway Awareness

Exclusive to the ST3400 is the implementation of the Virtual Approach Path^TM (VAP). Internally the ST3400 contains a synthetic glideslope to all runways based on FAA TERPS (terminal procedures). If the airplane is in a position to land and has FAA terrain clearances, the system is guaranteed not to alert - a very smart suppression method. This is something no other system does.

Observe that the ST3400 maintains awareness of the runway touchdown zones and not just the center of the airport.

ST3400 use of Runway Touchdown Zones to
determine aircraft intentions.

The ST3400 Benefit

What is the benefit of these exclusive features? A system that requires no pilot input for operation, yet enhances safety with the uncanny ability to know the aircraft’s intentions – and alert appropriately - even in the most demanding situations like circle-to-land operations and VFR flight. Runway Awareness and VAP's - a Sandel exclusive.

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