Digital Autopilot for Twin Otter Aircraft

Digital autopilot for Twin Otter aircraft is here. After several months working with Genesys (S-TEC) to gain approval for a new digital three axis autopilot, final flight testing was completed last month in Calgary, using one of Rocky Mountain Aircraft‘s Twin Otters.

The new system was put through its paces in all modes and aircraft configurations and performed flawlessly throughout the flight testing.

STEC 3100
STEC 3100 Installation

The FAA issued the STC SA09761DS on October 06, 2020.

With a list price of just under $25,000 for a full three axis autopilot, the 3100 is cheaper that the two axis limited functionality System 65 autopilot it replaces.

All the components are on condition only, eliminating the costly and time-consuming overhaul of servos that blighted the OEM Collins autopilots installation.

Digital-Flight-Control-System-DFCS
Genesys S-TEC 3100 Digital Flight Control System

The Details

The System is a digital three-axis attitude-based Digital Flight Control System (DFCS), and is designed for installation in aircraft equipped with a dual or single Air Data and Attitude Heading Reference System (ADAHRS), and/or DFCS computer internal sensors.

The System provides roll, pitch and (Optional) yaw modes along with an integral autotrim feature. The autopilot  includes a straight and level recovery feature, as well as envelope protection/alerting features.

The Programmer/Computer provides a means to engage the autopilot, select modes of system operation and to annunciate system modes and status. The Programmer/Computer consists of two sections: roll and pitch. The roll section accepts steering inputs from the navigation radios and the ADAHRS or internal sensors and uses this information to drive the Roll Servo. The pitch section receives signal inputs from the Primary Flight Displays and ADAHRS or internal sensors, and uses this information to drive the Pitch Servo. Yaw axis stabilization is provided by drive commands to a remote mounted Yaw Servo.

The Elevator Trim is automatically controlled by the Trim Servo, which also provides trim annunciation.

Twin Otter Autopilots

It may appear that Twin Otters and autopilots don’t mix. That would be the conclusion you would come to looking at a survey of the number of Twin Otters with an installed autopilot. So what is the history and why do operators shun autopilots in the Twin Otter?

The first production aircraft left the Downsview factory with an option for the Honeywell H-14 autopilot. This system used large pneumatic servos to control the aircraft. This was a popular option at the time however as the aircraft and autopilot aged the maintenance involved in keeping the system serviceable resulted in many operators disabling or removing the system. Other approved autopilot options followed, the Bendix M4-C, Collins APC-106 both these systems while having dispensed with the pneumatic systems and being fully electric still required regular scheduled maintenance to keep them airworthy, the regular overhaul of the servo’s being particularly onerous.

The last autopilot system introduced by DeHavilland was the Collins APS-65. Introduced in 1989 the APS-65 was one of the last analog autopilots designed prior to the shift to digital. This highly capable autopilot had one main drawback, it was hugely expensive and thus not a popular upgrade or option.

For operators requiring an autopilot, a retrofit autopilot was introduced by S-TEC, the System 65, this is a basic two-axis autopilot a lot less capable than the APS-65 but at a fraction of the cost. The System 65 has become the “go-to” autopilot for operators who need an autopilot since it was first certified in the
Twin Otter 25 years ago.

New state-of-the-art retrofit autopilots are being certified in many different airframes at an incredible rate.

Manufactures like Avidyne, Garmin and Genesys (S-TEC) are regularly expanding their approved model lists. The capabilities of the new digital autopilots compared to their 50 year old predecessors is vast, modern autopilot do much more than keeping an aircraft on a preset heading and altitude. They can almost fly the aircraft independently from take-off to landing. That capability should not be taken lightly. A pilot must still be completely aware of exactly what it is the autopilot system is or isn’t doing.

So why are these maintenance free, inexpensive, multi-function, safety enhancing autopilots still missing from Twin Otters?

It appears we have a chicken and egg situation here, no autopilot manufacturer is investing in a Twin Otter approval because there is no perceived demand among operators, but there is no demand because there are no systems available.

So who will break this impasse, which manufacturer will be the first to follow the “if you build it they will come” philosophy?

Well, the answer is Genesys Flight Systems who will be certifying their 3100 digital autopilots on one of Rocky Mountain Aircraft’s Twin Otters. Installation and approval are expected by the summer of 2020. A full review of the installed system, its performance and capabilities will be posted on this blog. Stay tuned.

Modern Technology – a Lifesaving Backstop in Aviation

Rocky Mountain Aircraft had staff attending Heli-expo in Anaheim this week.

Why would a company specializing in Twin Otter and other similar twin turbine aircraft attend a rotorcraft convention you may wonder? Well, plenty of equipment designed specifically for rotorcraft can be a great fit for the special mission Twin Otter conversions that Rocky Mountain Aircraft excels at. FLIR systems multi-mission audio, tactical radio suites, night vision cockpits for example, that started off exclusively for rotorcraft have been STC’d into Twin Otters.

Garmin Integrated Flight Display
Installed Garmin Integrated Flight Display

There was a lot of talk and speculation at the convention about the tragic crash that killed Kobe Bryant, his daughter, and seven others. While the cause of the accident is still under investigation, the lack of a terrain awareness system (TAWS) on the helicopter could have been significant.

The TAWS systems, mandated for the majority of commercial aircraft, are tried and trusted technology credited with saving hundreds of lives. It is also comparatively cheap to retrofit. A California congressman has now introduced a bill to make TAWS mandatory in all helicopters. What will it take before all aircraft owners and operators voluntarily carry out safety audits on their aircraft?

Universal Avionics Terrain Awareness (TAWS) Display
Universal Avionics Terrain Awareness (TAWS) Display

Modern avionics have made flying safer than ever, terrain awareness, traffic and collision avoidance systems, large graphical displays for situational awareness, real-time weather information have significantly reduced accident rates.

The latest generation of digital autopilots with their envelope protection, unusual attitude recovery, straight and level functions are so advanced compared to the old analog autopilots it’s like comparing a Sony Walkman to an iPhone 11. Automatic landing autopilots, in the case of pilot incapacitation, are now being introduced to the market.

While pilot training, proficiency, flying skills and good decision making along with a properly maintained aircraft are always going to be the primary safety feature of any flight. In the event of failure, modern technology should always be installed as the lifesaving backstop.

Garmin Product Announcements

Garmin came out of the starting blocks strongly in 2020 with two big product announcements.

First was their fourth generation navigator, the GTN Xi series. Powerful dual-core processors boost the GTN Xi series graphical display capabilities — with faster zooming, panning, and map rendering on the display. With almost double the pixel count of its predecessor, the GTN Xi series features wider viewing angles and one of the highest-resolution displays ever offered in this class of avionics.

Image of Garmin - GTN-750Xi
GTN-750Xi

Within a week, another product introduction. Garmin introduced the GI 275 Bright, reliable, high-resolution touchscreen instruments that offer all-purpose digital upgrades from traditional round mechanical instruments. As your primary flight reference instrument, GI 275 features an integrated display to support all the essential readouts — attitude, altitude, airspeed, and heading. Configurable for a multitude of functions

Image of  Garmin - ADI with Autopilot Integration

ADI with Autopilot Integration

For select aircraft and glass cockpit systems, GI 275 can function as a standby flight instrument with MFD capability2 for mapping, traffic, weather and more

Image of Garmin -  MULTIFUNCTION DISPLAY
Multifunction Display
Image of Garmin- Animated Nexrad
Animated Nexrad

ANIMATED NEXRAD

When paired with an optional GDL® 69 SiriusXM® receiver, the MFD-configured GI 275 offers display capability for satellite weather coverage with graphical NEXRAD imagery.

Image showing Garmin - Wireless Data Streaming instrument
Wireless Data Streaming
Image of Garmin - Radar Altimeter
Radar Altimeter

RADAR ALTIMETER

For applications that require precise tracking of aircraft altitude above the terrain, GI 275 can provide display capability for select radar altimeters, including the Garmin GRA™ altimeter series.

WIRELESS DATA STREAMING

Use built-in wireless connectivity to share data between the GI 275 and compatible mobile apps. Import databases. Stream weather, traffic, attitude information, EIS and more4.

Image of Garmin - Moving Map
Moving Map
Image of Garmin -  traffic and weather mapping
Traffic and Weather

MOVING MAP

Within the MFD configuration, a dynamic moving map page offers views of terrain features, airports, airspace boundaries, navaids, flight plan routings and more.

TRAFFIC AND WEATHER

With select ADS-B “In” datalinks, GI 275 MFD pages will support subscription-free U.S. weather and traffic displays, including TargetTrend™ and TerminalTraffic™ technologies.

As an approved dealer for Garmin, Rocky Mountain Aircrafts Avionics team can get you set up with the right configuration to support your aviation needs. Contact Us to see how we can help.

Transitioning from Radar to ADS-B

What is ADS-B you ask;

  • Automatic in the sense that it operates without external stimulus (unlike radar)
  • Dependent in the sense that the surveillance information is derived from onboard systems
  • Surveillance in the sense that it’s primarily intended to provide surveillance information to other parties
  • Broadcast because it transmits to all listeners without knowing who those listeners are, there is no two-way communication

The capability of an aircraft to transmit ADS-B signals is called ADS-B OUT, the capability of an aircraft to receive ADS-B signals is called ADS-B IN. The Garmin GTX-335 is an example of an ADS-B OUT only transponder, while the GTX345 is ADS-B OUT and ADS-B IN.

ADSB-how-it-works for ADS-B - Transitioning from Radar
ADSB-how-it-works – from FAA

ADS-B data contains information about the identity, position, altitude, and velocity of the aircraft. The position and velocity information is derived from GNSS (GPS).

ADS-B is a surveillance technology whereby the aircraft broadcasts information about its identity, position, altitude, and velocity of the aircraft to any interested party. The position and velocity information is derived from GNSS (GPS).

TCAS

ADS-B is not intended to replace TCAS, although in the future it will augment TCAS. The TCAS algorithm currently only uses distance and altitude to calculate whether there is a conflict and to determine the best conflict resolution strategy. With the more accurate ADS-B position available to the system as well, the number of TCAS interrogations can be reduced (the surveillance radio frequencies are getting congested in some areas) and the performance of TCAS can be improved. A new standard for this hybrid approach was published in 2013.

It may also be possible to have a passive TCAS-like system that does not require active interrogation but is purely depending on ADS-B. Currently, a technical standard for a new Airborne Collision Avoidance System (ACAS, the generic name for TCAS) is being developed in a joint RTCA / EUROCAE committee (RTCA SC-147 / EUROCAE WG-75), which will take advantage of more data offered by ADS-B. This new standard will eventually replace TCAS II.

ATC

The purpose of ADS-B is not to replace ground-based ATC. It will change the way ATC is done. ADS-B IN will improve the situational awareness of pilots; they will have a display of accurate positions of other aircraft. New procedures will allow pilots to maintain separation from other aircraft in marginal Visual Meteorological Conditions (VMC), where they currently would often lose sight of other traffic. More advanced usage of ADS-B will be flight deck based interval management (FIM) where ATC will be able to instruct aircraft to ‘follow that plane XX seconds behind for landing on runway YY’.

ADS-B is not a replacement for all radars, although it will allow the number of radars to be reduced. For remote areas that currently do not have radar coverage because of the associated high costs, ADS-B will be a cost-effective alternative.

The display of ADS-B IN requires a compatible cockpit monitor. The Garmin GTN series of navigators can display ADS-B targets blended with TCAS whereas older models of navigators and MFDs will only display TCAS traffic. The Garmin GTX-345 contains a built-in Bluetooth transmitter that can broadcast ADS-B traffic information to a handheld cockpit display such as an IPAD.

Canadian Maintenance Organizations (AMO’s) are approved under a bilateral agreement between the FAA and Transport Canada to complete ADS-B installations and return n-registered aircraft to service.

Rocky Mountain Aircrafts Avionics team can keep you equipped to stay airborne in 2020. Contact Us.