Tim Cahil

Mark A. Sleppy

Technical Fellow
BSAAE 1985






"It still amazes me and I feel so fortunate that I was able to attend a world class aero engineering school only two hours from my home, in my home state no less, to learn about the physics of flight.  It wasn’t that I learned all that I would ever need to know, but rather that my professors built a solid foundation, giving me the tools and experience that I would need for a good start at being successful after I left these hallowed “red brick” halls of learning."

Mark A. Sleppy is a Technical Fellow and Boeing Designated Expert in Boeing Commercial Airplanes (BCA), Loads & Dynamics (L&D) group of the Flight Sciences organization.  He is L&D’s technical leader for advancement of aerodynamic testing technology, computational fluid dynamics (CFD) and aerodynamic model development.

Mark was born and raised with three siblings on a small farm near Goshen, IN.  His father, Richard, a car mechanic and Korean War veteran and his mother, Jane, a twenty-four-seven homemaker, were both born and raised in or near Goshen.  He spent many sunny days flying model airplanes and rockets in the surrounding fields and sadly losing a few in the late summer corn.  He built a small wind tunnel in the barn, replete with manometer board for airfoil surface pressures, using bits of this and that.  He still has vivid memories of watching Neil Armstrong on a black and white TV take that first step and of getting up early while in college living at Shreve Hall to watch STS-1 / Columbia launch but cannot remember when he didn’t have a love of things that fly.  He graduated with honors from Goshen High School and applied to only one university, Purdue, to follow his dream of being an aerospace engineer.

Mark graduated from Purdue University with a Bachelor of Science in Aeronautical and Astronautical Engineering and six Co-Op sessions with Bell Helicopter in December 1985.  Though the course work at Purdue was very challenging, as it should be, he has many fond memories of his time on campus and of the Professors who set the foundation for his career.  But the memories he cherishes the most of his time at Purdue are those from working with his senior design team on a forward-swept wing fighter concept in AAE 451 taught by Professor Emeritus George Palmer.  To top this off, he is still thrilled to have been able to build and test a wind tunnel model of that design for AAE 452/490 with fellow team member David Denney under Prof. Palmer’s instruction.

He joined Boeing in early 1986 to work in the Static Loads group on the 747-400 program with responsibility for external loads analysis to meet Federal Aviation Regulations part 25.  His first assignment was the analysis of loads on the vertical tail rear spar after the redesigns in the tail section following to the JAL accident in 1985.  He worked for ten years as a static loads engineer on many BCA programs up through the Next-Generation 737 program.  During this time period, Mark was a key figure in the successful development and implementation of Boeing’s first fully integrated aeroelastic analysis tool. 

In 1995 Mark was recruited for L&D’s new Aerodynamic Test & Database team and he has worked on the development of improved aerodynamic modeling for aeroelastic analysis on every new BCA program since, most recently overseeing the 777X Loads aerodynamic database development.  In 2006 he was recognized for his technical expertise and promoted to Boeing Associate Technical Fellow, the first of three levels of senior technical leadership in the non-management career path at Boeing.  As Principal Lead of the recently merged Aerodynamic Testing and Database and High Lift Static Loads teams he continues to lead and mentor the group members in the best practices of aerodynamic modeling for loads for new programs like the 737 MAX and 777X.  Mark regularly represents BCA Loads and Dynamics on Boeing enterprise wide teams for advancements in aerodynamic modeling, wind tunnel testing, flight testing and CFD.  In 2016 he was promoted to the second level of the Technical Fellowship in recognition for his expanding technical role and greater sphere of influence.

Throughout his career Mark has been heavily involved in research and development for improvement of the aerodynamic modeling used in BCA aeroelastic analyses. For over a decade he has been the Principal Investigator for internal application development in wind tunnel testing and data reduction technology and the advancement of utilization of CFD within BCA Loads and Dynamics.  He has most recently led projects that yielded break through methods in static aeroelastic analysis and dramatically improved wind tunnel to flight correlations.  Along these lines, he initiated a two year collaboration project between Boeing and Purdue to investigate methods for merging multi-fidelity, multi-source aerodynamic data sets for aircraft design and analysis.  The team included many Boeing consultants and eleven Purdue researchers, both professors and graduate students.

Outside of Boeing, Mark is a Senior Member of AIAA.  As a Boeing representative, he has attended a number of conferences and workshops like the SFB 401 HIRENASD Workshop at RWTH-Aachen - University of Technology.  He has observed advanced cryogenic wind tunnel testing methods at the National Transonic Facility at NASA-Langley and the European Transonic Wind tunnel at Cologne, Germany.  He was invited to give a presentation at the 47th AIAA Aerospace Sciences Meeting in ’09 entitled, “The Integration of Wind Tunnel Testing and CFD for Aeroelastic Analysis at Boeing Commercial Airplanes.”  In addition, he presented a paper at ASM ’09 which he co-authored on the Boeing-NASA collaborative research project that he led entitled, “Investigation of Seal-to-Floor Effects on Semi-Span Transonic Models”, (AIAA Paper 2009-619).

Mark is married to Lisa, has three adult children; Naomi with her husband Thomas, Josiah and Anna and two cute granddaughters.  He still enjoys hobbies involving anything that flies and recently took his first hang gliding lesson on the sand dunes near Kitty Hawk, NC.  He is an avid, one might say voracious, reader and loves to learn about and travel to historical and ancient destinations.  Above all, he is thankful for the grace of God through Jesus Christ.