Aircraft Systems and Flight

Flight Control System

Flight Control Systems consists of flight surfaces such as ailerons, rudders, and elevators; however, they also consist of springs, bell cranks, and pushrods.  While there may be failures in a flight control surface, many failures can be traced back to the flight control linkages that connect cockpit controls to flight surfaces.

Indications of flight control system failure may include:

• Binding in the controls or lack of free movement
• Unresponsiveness of aircraft with cockpit control input
• Loss of controlled flight

Potential causes of flight control failure:

• Foreign objects can become lodged in the control system and restrict movement
• Maintenance failure that could include improper maintenance or parts installed incorrectly
• Failure in the linkage, bearings, or control rods

A specific flight control failure that I am familiar with is the Swashplate Duplex Bearing Failure in the CH-53E Super Stallion.  It is pictured below removed from the aircraft.

In 1996, a CH-53E Super Stallion crashed at the Sikorsky factory in Stratford, Connecticut killing four Sikorsky employees while it conducted test flights prior to government delivery.  The crash was attributed to a failure of the duplex bearing in the swashplate.  The manufacturer, Kaydon, discovered there were issues with the quality of the plating on the bearings, which caused the swashplate to seize in flight.  As you can see from the example picture below, a bearing failure between the rotating and non-rotating plate would result in loss of rotor control.

The mitigation for what would be referred to as a “quality escape” in today’s logistics terminology, was the replacement of 200 swashplate assemblies at the cost of roughly 30 million dollars.  Additionally, an in-flight Bearing Monitor System was developed and installed to check for bearing heat and vibration to monitor for impending failure in all phases of flight.

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References

Federal Aviation Administration (FAA). (2016). Pilot’s Handbook of Aeronautical Knowledge (PHAK). Retrieved https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/

Harr, D. (1996, June 27). Jury probes maker of part blamed in Sikorsky crash. Hartford Courant. https://www.courant.com/news/connecticut/hc-xpm-1996-06-27-9606270194-story.html

Hess, P. (2000, August 29). Six White House helicopters grounded by Marines. United Press International. https://www.upi.com/Archives/2000/08/29/Six-White-House-helicopters-grounded-by-Marines/8989967521600/

Rotaru, Constantin & Todorov, Michael. (2018). Helicopter Flight Physics. Intech. http://dx.doi.org/10.5772/intechopen.71516

Operating Environment and Aircraft Performance

Atmospheric Pressure

Atmospheric pressure is different than many of the other environmental factors for aviators.  Because it is not easily seen, like precipitation, atmospheric pressure can be (and has been) a contributing factor in aviation mishaps.  

Pressure altitude is the term used when referring to the height above the standard sea level pressure (SDP or Standard Datum Plane).  The standard atmospheric pressure at sea level is 29.92 ”Hg or 1,013.2 mb (pictured below).  In the cockpit of an aircraft, 2992 is dialed in to the barometric altimeter when above a certain altitude.

When high pressure altitude is combined with other factors, such as high temperature and high humidity, the result can be what is known as a high density altitude (Goodman & Small, 2018).  

Chapter 4 of the Pilot’s Handbook of Aeronautical Knowledge states: 

“Density altitude is pressure altitude corrected for nonstandard temperature.”

A simpler way to say this is – It is the atmospheric pressure that is corrected for:

• Field Elevation
• Temperature
• Humidity

This means the runway that is listed at 6,000 feet on the chart supplemental may not feel like it is at 6,000 feet when operating an aircraft because the plane could behave like it is at 10,000 feet once the other factors affect the aircraft.  

Those factors include:

• Decreased lift – thin air means less fluid passing over and around the wing
• Reduced engine performance – the engine is receiving less air to the compressor
• Reduced thrust – the propeller produces less thrust with less fluid to push or pull

A good mitigation strategy in order to prevent aviation mishaps include:

• Proper mission planning (know the conditions of the airfield)
• Plan take off and landings when the Outside Air Temperature (OAT) is at its lowest point
• Plan for longer distances to take off and land (see chart below) to compensate for higher velocity to offset reduced lift (see chart below)

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References:

Federal Aviation Administration. (2019, February 22). Mountain Flying and High Density Altitude in 57 Seconds [Video]. YouTube. https://www.youtube.com/watch?v=k1qylDKtr6M

Federal Aviation Administration. (2016). Pilot’s Handbook of Aeronautical Knowledge (PHAK). https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/

Goodman, C. J., & Small Griswold, J.,D. (2018). Climate Impacts on Density Altitude and Aviation Operations. Journal of Applied Meteorology and Climatology, 57(3), 517-523. http://dx.doi.org/10.1175/JAMC-D-17-0126.1

Ethics in the Profession of Aviation

Getting it right the first time, every time, is exceedingly difficult to accomplish.

In the profession of fixing and flying aircraft, that is exactly what we attempt to accomplish every day for each sortie generated and for every flight schedule executed.  If the pilots, maintainers, technicians, aircrew, and controllers fail to get it right, the cost can be high.

 The picture above was taken in Iraq in 2006 executing Casualty Evacuation in the Sunni Triangle.  The squadron executed 6,260 flight hours in a six-month deployment with zero missed missions.

Ethics - a set of moral principles: a theory or system of moral values. (Merriam-Webster, n.d.)

In an engineering study of failure analysis, it was discovered that 26 percent of aviation related accidents can be traced back to an event that was caused during maintenance.  Roughly 85 percent of those failures involve an omitted procedure or faulty installation of components (Usanmaz, 2011).

Meeting high standards requires having highly qualified and certified people.  Ethics plays a large role in setting standards and qualifying/certifying people.  During my time in aviation, most of the issues I have experienced with pulling an individuals qualification or certifications stemmed from unethical behavior that was manifest in the work environment.  Failure to maintain a process, shortcutting published requirements, or being untruthful about accidents all boil down to a breakdown of ethics in an individual’s system of values versus the organizations required system of values.

Ethical behavior and exhibiting ethical virtues are important in holding the high standard expected to always get things right.  There are plenty of other failures (material failure of a Gearbox Input Freewheel pictured above) that the aviation industry must worry about without questioning the ethical virtues of the crew, maintainers, and air traffic controllers. 

References

Merriam-Webster. (n.d.). Ethic. In Merriam-Webster.com dictionary. Retrieved January 12, 2022, from https://www.merriam-webster.com/dictionary/ethic

Usanmaz, O. (2011). Training of the maintenance personnel to prevent failures in aircraft systems. Engineering Failure Analysis, 18(7), 1683-1688. https://doi.org/10.1016/j.engfailanal.2011.02.010.