TACTILE WARNINGS IN TODAY’S MODERN COCKPITS

Engine Exceedance Monitoring Utilizing Stick Shakers

Adrian Rosenberg Manager Helicopter Programs Safe Flight Instrument Corporation White Plains, NY [email protected]

Abstract In general terms this is a method of alerting pilots to engine or airframe exceedances by using tactile feedback as opposed to visual or audio warnings. Studies have shown that response time is quicker and more effective by using tactile warnings. Too many warnings are missed or corrected for too late by using visual alerts due to pilot workload. If the pilot can recognize and react to warnings quicker a significant savings in engine repairs will result leading to fewer mechanical failures and premature maintenance events directly leading to safer helicopter operations so saving lives and revenue.

Introduction

Information monitoring in aircraft is getting more complicated with the increased number of audio and visual warnings. Today’s pilot has a lot of input coming his way. A large variety of horns, gongs, flashing lights and voice over warnings inundate today’s cockpit.

Tactile feedback is another method of providing pilots with a warning without introducing further audio or visual alerts to a pilot’s workload. Distributing information more evenly across the available senses, many of which may be currently under-utilized, is an alternate method to meeting this requirement (Figure 1).

Figure 1. Shaker Illustration

A human-factors study from Ohio State University has found that pilots prefer being vibrated to having visual or audio alerts presented to them.

In the study in Ohio, it was found that pilots are more likely to notice alerts through tactile cues (identifying up to 40% more alerts) and react faster to such stimuli. In tests performed it was found reaction time from audio to tactile cues is almost twice as fast in favor of tactile warnings.

In an already crowded warning panel a tactile alert is a welcome addition to expand the number of sensory channels available to which information arrives to the pilot while reducing demands on any one channel.

Tactile cues are a good alternative to improve the saturation threshold of a pilot.

The Product

Safe Flight has developed a system where by signals from the engine and transmission are routed to a comparator computer on board and compare in real time what the actual indication is compared to a predetermined factory authorized setting. Any time the actual value is greater than the authorized factory setting, a signal is sent to a stick shaker mounted on the collective control (Figure 2). The control is in the pilots hand and his immediate instinctive reaction is to lower the collective, unloading the rotor disc and reducing power needed from the engine. In normal conditions this will result with engine parameters falling back to the normal operating range.

Figure 2. Shaker Installed in Bell 206B3

The reaction time is less as compared to audio or visual warnings as the warning is in the pilot’s hand resulting in one less step for the brain to react to. In an audio or visual alert the brain has to process the information and direct the input to the hand, the hand then has to take a corrective action. This method eliminates some of the brains work and studies have proven reaction time to be twice as fast in some cases.

By taking such signals from engine torque, engine exhaust gas temperature, engine gas producer speed and rotor speed; it is possible to route all exceedances to a specified channel in the computer and any time any one value is exceeded the shaker will go off in the pilots hand (Figure 3). It will not tell him which value he is exceeding, but that he has approached an engine limit now and needs to reduce collective to get back to the normal operating range.

Figure 3. Exceedance Warning System Diagram

Warning: Low Speed High Speed Shake Shake

EXCEEDANCE Warning Signal

Control Ng

If the pilot has his head out of the cockpit and is not looking at the gauges or warning lights he will be advised by tactile cues, reduce the collective, get his head back in the cockpit and continue flight having averted a lengthy over torque or over temp.

The computer is adjustable so the warning may be set at a desired level required by the operator in conjunction with the manufacturer’s recommendations.

Two speeds are available. First a low speed warning to advise a pilot that he is approaching a limit and then a second higher speed shake activates when he reaches the limit.

The shake is advisory in nature and in no way prevents the pilot from flying the helicopter at the limit if emergency conditions require the pilot to be there. It does not impede control movements and pilot can override the system at any time.

Projects

Stick shakers have been used for many previous designs created by Safe Flight in particular stall warning/stick shaker applications in commercial jets and corporate aviation. This system takes proven technology derived from many years of use in the fixed wing industry and applies it to rotocraft technologies. The system is presently installed on Eurocopter Gazelle SA341G, Bell 430 (part of the TC), Bell 427 option and Bell 206 B3 by STC.

Currently in final stages of installation on the Bell TH57 for use at the Naval Aviator training school in Pensacola Florida.

Also it is in early stage development for the AH64D Apache helicopter and simulator in Huntsville Alabama in a project with Boeing Helicopters.

Conclusion

The main advantage of the Exceedance Warning System is the real time warning to the pilot while flying in many types of operations where attention is diverted from the gauges for short periods of time.

Unlike a HUMS exceedance monitoring system that advises the pilot when limits have been exceeded and not before they have already exceeded the limits. This is discovered after the flight when maintenance downloads the data from flight. Data from a study showing the effect of overtorque and overtemp to the US Army in the period of 1984-2004 (Figure 4):

Figure 4. Army Safety Data 1984-2004 Chart

OVERTORQUE # Fatal Injury Damage Injury TOTAL Average A/UH-1 56 2 20 $18,281,728 $935,367 $19,217,095 $343,162 A/MH-6 13 2 $3,539,847 $423,600 $3,962,447 $304,881 AH-64 21 5 $71,858,984 $80,725 $71,939,709 $3,425,700 CH-47 1 $20,000 $20,000 $20,000 OH-58 54 $9,161,945 $9,161,945 $169,666 M/UH-60 11 9 3 $19,291,972 $4,775,386 $24,067,358 $2,187,942

OVERTEMP # Fatal Injury Damage Injury TOTAL Average A/UH-1 30 3 $259,188 $20,825 $2,613,013 $87,100 A/MH-6 8 $304,648 $304,648 $38,081 AH-64 5 $939,187 $939,187 $187,837 CH-47 13 $1,295,537 $1,295,537 $99,657 OH-58 67 $2,469,527 $2,469,527 $36,859 M/UH-60 10 $731,995 $731,995 $73,200

Safe Flight’s Exceedance Warning System allows pilots to fly to their limit while doing sling work, normal operations or heads out the cockpit operations. This reduces the number of costly inspections. The results will be seen in the lower number of mandatory inspections required to be performed on engines after over torques and over temps resulting in saving lives as well as dollars.