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Unless you are starting the ‘refurbishment’ of a Supersonic aircraft- you will have to understand that dynamically- your airframe will likely contract (change shape) at altitude- due to the frigid temperature (-60°F) normally encountered in the upper flight levels. A Supersonic aircraft will do the opposite- i.e. stretch because of the frictional heating.

AvBuyer   |   1st August 2010
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Issues To Consider/Pitfalls To Avoid:
Don’t get caught-short when time comes to refurbish the cabin.

Unless you are starting the ‘refurbishment’ of a Supersonic aircraft- you will have to understand that dynamically- your airframe will likely contract (change shape) at altitude- due to the frigid temperature (-60°F) normally encountered in the upper flight levels. A Supersonic aircraft will do the opposite- i.e. stretch because of the frictional heating.

I will never forget that when I was an apprentice aircraft mechanic- one of my mentors was a retired Concorde flight engineer. He amazed me with the fact that while on the ground- the space between his flight engineer panel and bulkhead was barely the thickness of a piece of paper- but at FL500 and at Mach 2- he could put his fist between both fixtures. Conversely several times while riding along in various aircraft that had been established in cruise flight for a long duration- i.e. cold-soaked- I have gained access to the cabin-side of the exterior skin and observed that all of the fasteners and the edges of the skins- frames- longerons and stringers- were all furred with a continuous film of ice crystals.

Why am I mentioning all of this at the start of an article that discusses Interior Refurbishment- you may ask? Well you must believe me that if you are planning on making any radical configuration changes with an existing interior- or in-fact you are planning to take the long and arduous path of designing a totally new interior and having it certified under a Supplemental Type Certificate (STC)- or the like; if you fail to consider the dynamic changes that the cabin superstructure shall undergo- within the parameters of sweating from the sweltering heat of the sun while sitting on the ramp- to the opposite extreme of becoming cold soaked at altitude- I am afraid that you will be plagued with sticking and wedging doors- drawers- tables- cracked countertops- etc. ad-infinitum.

If you stay with the interior design and configuration that your aircraft was originally delivered in- the chances are that you won’t fall foul of some of the nasty perks that result from ‘bad re-designs.’

If you do choose to start fresh with a ‘baretube’- it is better now (before you start) to ask yourself the question “How am I to safely- legally and efficiently allow conditioned- pressurized air to enter- circulate and exit the cabin spaces of my aircraft?

Especially you must not forget to incorporate suitable ‘blow-out’ doors and panels that will prevent the entire bulkhead and cabin shell structures from being wrenched from their mounts as the air pressure behind them attempts to cascade out of the leak area- during the unfortunate phenomenon posed by an explosive decompression while engaged in high-speed and high-altitude cruising flight.

Most business aircraft operate with a cabin pressure maximum differential of 9 psi. The International Standard Atmosphere cites 14.7 psi being the standard air-pressure at sea level. At altitude the air-pressure drops to about 5 psi. If the pressurized areas of the cabin can’t be fed efficiently- then various problems will arise- including in the most minor form being whistles- rasps- farts and other sounds of air constriction. These noises are not a big deal in a cargo aircraft- but it is a big problem within the confines of an executive passenger cabin. Also the conditioned air must be able to circulate in and out of the cabin- thus bringing fresh air in and stale air out- with a minimum of recirculation- therefore all air passageways must be up to the task that the Original Equipment Manufacturer (OEM) had designed into the system.

Staying with the issue of noise- when you have the interior furnishings and shell removed from your fuselage ‘tube’- now is your absolute best time to replace and/or upgrade your acoustic and thermal insulation blankets.

Back in the early days of business aircraft- insulation blankets were often heavy- bulky- moisture trapping affairs that had the characteristics that were akin to simple bed quilts. Today’s high-tech- lightweight- fire and mould proof systems are factors apart from their grandparents- and in some applications are able to block and trap 80-90% of all exterior noise as well as the same levels in heat-retention.

I remember years ago that we pulled almost 200 lbs of old lead-vinyl insulation out of a Sabreliner- and replaced it with a system from E.A.R. that only weighed 30 lbs- and was 10 times more efficient than the nasty- heavy stuff it replaced.

A word of caution though- to any who believe that they will just buy a roll of the new insulation- and just roll it in- cut to size and secure it with pit tape and ty-raps: This is a false economy- because you might trap and retain heat better than before- but you are likely to have a noisier cabin. Why? Talk to any of today’s insulation blanket manufacturers- and there is a high probability that they have already performed an exhaustive sound test on your model of aircraft- and in turn- they have developed and had certified a complete insulation package system that is customized to return maximum performance to you.

If they don’t have a specific package for your aircraft- there is a very high probability that they will instrument and analyse your cabin interior and custom make a system for you anyway. Most of the passenger and interior loads are distributed into- and carried by the cabin floor structure. It is imperative that before you start redesigning the layout of your cabin’s interior- you must first know what the structural floor loading capacity is- and where the load distribution zones are. A Designated Engineering Representative (DER) will be able to assist you here. Remember that often the same load factor will not apply to all areas of your cabin floor- especially in areas where there are no seat-tracks or tie-downs installed.

Two other areas of concern that are often glossed over by some of the discount- or ‘mom and pop’ shops are “G” Rating and Aisle Width Clearances. If you plan to replace your old ‘type-design’ seats in your cabin with lighter-wider-modern-look designs- you need to be cognizant of the fact that:

1. You will be changing the original type design and therefore you will fall under the new rule- which affects aircraft built after October 2009 (requiring all seats must be able to withstand 16 times the force of gravity- compared with the 9g standard that had been required since 1952). The floors and the tracks the seats ride on also must be able to withstand 16g loadings. I have seen many couches- kibitzer- and credenza seats that add utility to an interior once in the air- but are not certified seats because they are not for use during take-off or landing.

2. Your aisle width clearance- i.e. the distance between the seats- down the centre or passenger aisle walkway- must conform to the newer requirements of cfr 14- FAR 25- which for 10-or-less passenger seats requires 12 inches of clearance from floor level up to 25 inches above the floor- and then 15 inches above this level. If your aircraft is certified for more passengers- then your aisle clearance requirements also increase. I have often seen small and midsize jets that have been upgraded with new- or re-upholstered seats that don’t even come close to meeting these width requirements- especially in some aftermarket Hawkers and Falcons.

Staying with the topic of seat upholstery- most aircraft type designs now require that when a seat is re-upholstered- the stitching type- mechanical design- pattern and placement- foam specifications and leather or fabric materials must all go back configured exactly as they were before; otherwise the seat won’t be able to meet the 16g requirement that it was originally certified with. It might be nice to pick out a new sew pattern- padding and design of a seat in another aircraft type featured within the pages of World Aircraft Sales Magazine- but be very wary of having your local interior shop adapt a duplication of this design in your aircraft- as you will likely be changing the type design that was certified in your aircraft. When in doubt call a DER.

In the cfr 14- FAR Part 25 regulatory world of Transport Aircraft- the issue of materials flammability is well known and the regulations are followed usually to the “tee.” Unfortunately cfr Part 43- Appendix A which is titled in-part: “Preventative Maintenance” to some extent contradicts the logic and safety that is meant to be followed.

It states that “...(11) Repairing upholstery and decorative furnishings of the cabin- cockpit- or balloon basket interior when the repairing does not require disassembly of any primary structure or operating system or interfere with an operating system or affect the primary structure of the aircraft.” Even though this is really meant to be applied against small and light aircraft (in my opinion)- some owners or small shops take advantage of this poorly chosen language and use this portion of the federal regulations to recover their own seats- on the cheap. Often they forget that the flammability burn testing requirements still need to be met- regardless of the fact that the materials purchased had been ‘batch-burnt’ for conformity- and therefore are not meeting the safety requirements set by the FAA.

I often consider that our segment of the General Aviation industry – Business Aviation - is really a boutique- with the definition of the word Boutique meaning ‘one of a kind.’

Nowhere does this term apply more than with the design and completion of a business aircraft interior. Until the best shops started using Computer Aided Design and Manufacturing (CAD/CAM) to cut their bulkhead and cabinet components from digital design patterns- there was a better chance of finding a DNA match with yourself and a gorilla in Borneo- than you would have in finding a drawer- or door that matched another business aircraft at another airport.

There is immense pride both in the making and the ownership of a beautiful wood or carbon composite finish on interior cabinetry. There is no loss of craftsmanship- if the basic shape that the artisan cabinet maker and woodworker begins with- has been precisely cut by a robotic knife or laser. At least now- when a briefcase or other luggage smacks into a galley front- the aircraft owner’s director of maintenance can call up the completion shop and order by part number from the drawings that came with the interior- a replacement door front- which is guaranteed to fit.

Now that I have mentioned ‘drawings’- it is a good time to expand on this area of interior refurbishment or completion. Time- and time again I have seen interior or avionics upgrade projects over-run their promised dates and quoted prices (by significant margins)- all because the owner/operator had lost the wiring diagrams for their aircraft.

Having said that- the sad reality is that- just like my statement about most business aircraft being boutique equipment- virtually all older aircraft (older meaning that they have been through several ‘refurbs’ and upgrades) are now highly unique and won’t conform to the wiring manuals that they originally came with.

Interior shops start pulling handfuls of their rapidly thinning hair- when they are finding and chasing unidentified wires that shouldn’t be there- or worse yet- should be there- but again- they are not. It is not uncommon for an installer to lay down a fresh wire for a new or failed system- instead of removing and replacing the original wire. This is one of the reasons that aircraft generally gain weight over time. The true impact of this practice is never really felt until it is time to pull out the interior for refurbishment - at which point- the games begin! So regardless of what you may hear- never ever lose your wiring manuals. Treat them with as much vale and respect that you give to your log books.

Another area of confusion for many owner/operators that hope to upgrade their interior comes from what audio/visual/entertainment and communications systems that they can put into their aircraft. Sometimes it really is as simple as going down to Best-Buy and buying an Underwriter Laboratories (UL) Approved- high-end flat screen LCD monitor- DVD- or MP3 player. You must then somehow legally and safely transition this piece of consumer electronics out of the box- and mount it in your aircraft.

FAA Advisory Circular number 25-10 which is titled: ‘Guidance for Installation of Miscellaneous- Non-required Electrical Equipment’- sometimes provides an installer with enough authority to get a non-Technical Service Order (TSO) or non-Parts Manufactured Approval (PMA) item- installation approved. But once you start looking into the requirements laid down by The Radio Technical Commission for Aeronautics (RTCA) document DO- 160E- which is titled: ‘Environmental Conditions and Test Procedures for Airborne Equipment’- you might have your plan go a little wobbly.

This expansive and vital document details the “Standard procedures and environmental test criteria for testing airborne equipment for the entire spectrum of aircraft from light general aviation aircraft and helicopters through the “Jumbo Jets” and SST categories of aircraft. The document includes 26 Sections and three Appendices. Examples of tests covered include vibration- power input- radio frequency susceptibility- lightning- and electrostatic discharge.

DO-160E is recognized by the International Organization for Standardization (ISO) as de facto international standard ISO-7137. So truly- when you are in any doubt- call both a DER and a Designated Airworthiness Representative (DAR)- who will lead you through this minefield. Don’t forget that there are many systems available out there that are already TSO- STC and/or PMA approved for installation into your aircraft.

Much of what I have highlighted above has probably given-you a mental picture of what an ideal refurbishment and completion shop will look like to you. When you are choosing who you will spend your money with when it is time to re-do your interior- hopefully the shop that you select- will have a Repair Station Certificate- a long list of satisfied customers for you to reference- an in-house engineering department that can produce the wiring and maintenance manuals that you will need after their work has been completed. The better shops will also have their own DER and DAR on-staff- and in some cases they will also be an FAA Designated Alteration Station (DAS).

A ‘word to the wise’ regarding ‘cheap-fixes’ for a worn interior: Please be very- very- very cautious if ever you elect to have your leather seats- sidewalls and armrests re-dyed instead of replacing them.

Certainly there are viable shops out in the marketplace that can give you an excellent re-dye job that won’t give you any foreseeable problems with their work later on. However you must be aware that some Aviation Authorities like the European Aviation Safety Agency (EASA) will not allow or accept aircraft that have re-dyed leathers within- believing that it constitutes a type-design change- and therefore is disqualified for continuing airworthiness approval- unless re-tested through the flammability testing procedures again.

Another reason is the feint possibility that the CEO or Chairman’s wife is riding on board the aircraft after you have had the seats dyed- and she is wearing a white pants suit… When she reaches her destination- to her horror she finds that her trousers have now changed to the color that was sprayed- rubbed or painted onto the seats earlier. Now that is a bad day!

I almost forgot! One problem that you may run into if ever you are reconfiguring the layout of a business aircraft cabin- especially if you are removing or resizing cabinetry (and this has happened to me before)- is never forget where you are going to stow the life-rafts. It is totally ‘un-cool’ to be left with a gleaming new interior- and find that the only place for the life rafts is between the lean-backs of back-to-back seats! That’s another really- really bad day.

And my final word is this: There is absolutely no reason on this earth- that you should be putting fluorescent tube lighting systems back into a cabin during a refurbishment- and especially during a completion. Light Emitting Diodes (LED) is the only way to go these days. Forget hot- heavy and fragile fluorescents- and see your interior in a new- better light instead!

Of course if you have any questions regarding this material that I have laid out on the pages of this fine magazine- you are always welcome to call me direct on the following telephone number: +1.636.449.2833- or via my email:
[email protected]

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