Complexities of Composites

Guy Norris’ “Some Assembly Required” (May 21-June 3, p. 27) was very informative, but left me wondering why the Boeing 777X wings are called the “world’s largest all-composite wings” when 45 metallic ribs are in each wing and the wingbox extensions are metallic.

Al Merino, New Bern, North Carolina

(The reader correctly observes that, so far as the composition of the 777X structure itself is concerned, the wing includes several metallic parts, including ribs and the extended wingbox. But from Boeing’s perspective, the structure is considered “all-composite” because the primary load-carrying elements of the wing—the spars, stringers and skins—are all made from composite materials—Ed.)


End of the Road for PC-6

The demise of Pilatus’ PC-6 prompted reader comments (May 21-June 3, p. 6) suggesting that someone should take over its manufacture. I agree that with aggressive marketing and possibly a lower manufacturing cost, it could be a viable program.

Over a decade ago, when Pilatus was building about one per year, I approached the company with just such a request. Their response was an emphatic “No!”

Charles J. Jennissen, Sherwood Park, Alberta

UAS Certification Standards 

From 2004-13, I provided contract support to the FAA’s air traffic unmanned aircraft office. My duties included updating the Certificate of Waiver or Authorization (COA) process to enable greater access to the skies for unmanned aircraft, as well as adapting the FAA’s Safety Management System (SMS) to assess risks associated with unmanned aircraft operations in the National Airspace System.

I therefore follow with interest Uber and other organizations’ ambitious and exciting visions of the future (May 21-June 3, p. 20). However, it is what is lacking in the present UAS framework that gives me concern.

I see serious deficiencies in how UAS are to be certified as “airworthy,” especially with respect to their propulsion and navigation systems, data links and conflict detection and resolution software. The primary reason the COA process is still required is that more and more designs are being approved for flight without standardization or structure in these areas. 

For unrestricted (“integrated”) operations in the advanced visions currently being proposed, these and other issues must be resolved. What is the current status of these critical elements? For that matter, what are the FAA’s UAS certification standards?  

Separately, the many disconnects between the two parts of Title 14 of the Code of Federal Regulations that govern manned versus small unmanned aircraft—Parts 91 and 107, respectively—have led those parts to conflict with each other in significant ways. Realistically, present-day UAS operations cannot comply with Part 91, and relief from many of its provisions still remains necessary through the FAA’s COA and SMS processes. 

Part 107 represents the FAA’s efforts to comply with the expressed will of Congress to get at least some UAS in the air as quickly as possible on a regulated basis. That this activity had to be limited to only those unmanned aircraft weighing less than 55 lb., and that virtually all of its provisions except that weight may be waived on request, demonstrates just how fragile the current regulatory structure for UAS truly is. Finally, Part 107 has been rendered obsolete and will not meet the needs of future UAS operations.

The future for UAS flight is unlimited, but the devil is in the details of the new regulations and procedures that will be needed to allow the sector to reach its full potential while preserving safety.

Maurice Connor, Virginia Beach, Virginia

Energized PFD? 

Am I the only one to wonder what flight condition is shown on the Airbus harmonized primary flight display (PFD) that accompanies “Airbus Introduces HUD Symbology on Primary Flight Display” (June 4-17, p. 62)? Attitude 2 deg. nose up, flightpath 7 deg. up and accelerating? Is this a massive updraft, a B-52 with takeoff flap or the immediate aftermath of a sudden lunge forward on the controls?

But seriously, it is good that Airbus includes yaw and heading information on the PFD (the marks along the horizon line). Jimmy Doolittle asked Elmer Sperry for just such a display in the 1929 Guggenheim “blind flight” project, but Sperry convinced him that separating direction from attitude in two instruments would be easier to interpret. I suspect he also figured a single three-axis mechanical instrument might be tricky to make. Of course, we have no such worries in the digital age.

Alex Fisher, Chacombe, England