Fuel Cell Capacity PA-24

[Zach Grant L1011jock]

I wrote this in response to a thread on the COF. I think it bears repeating here as it explains what is really going on regulatorily with the fuel capacities and unusable fuel in the PA-24 250/260 main tanks.


1. Whereas the TCDS dictates the design/equipment/and authorities by which an aircraft is certified.

2, Whereas the AFM is regulatory and is an extension of the TCDS as it is required by the TCDS.

3. Whereas the POH is not regulatory, however it is published by the "most expert witness" ie. the Piper Aircraft Co.

If none of the regulatory documents specify a particular placard, then one must find a regulatory requirement for the placard, or else it is simply an advisory statement given by the "most expert witness", and has no regulatory implications, but could have civil implications when disregarded.

CAR 3 Certification stds (the reg the aircraft was certified under)has this to say:


§ 3.767 Fuel, oil, and coolant filler openings. The following information shall be marked on or adjacent to the filler cover in each case:

(a) The word "fuel," the minimum permissible fuel octane number for the engines installed, and the usable fuel tank capacity. (See § 3.437.)
Based on this, it appears that the requirement/methodology for placarding a fuel tank is found in the certification stds of the aircraft as stated in the TCDS (CAR 3, effective November 1, 1949, including Amendments 3-1 through 3-12, effective April 13, 1954), and as such the cert stds refer us back to the certified usable fuel as stated in the TCDS.

In this case, since the Administrator has signed off on the TCDS, as well as the AFM (as being approved and required under the TCDS), and has essentially agreed with the "most expert witness" that the documentation contained in those documents is true and correct, then all that is contained in the TCDS, and thusly the approved flight manual is correct, regardless of inconsistancies within the documents. Changing any would not be legal without concurrence that the stated data was in error, and a correction issued by the "most expert witness" as well as the certifying authority, the FAA Administator.

The TCDS becomes the controlling documentation for the required placard of the fuel opening as referenced in CAR 3. Thusly, I would argue the correct placarding of the main tanks of PA-24 aircraft is as follows:

PA-24 (180).........91/96 min Octane 30 USG (30 is the capacity as well as the total usable in the 180).

PA-24-250 S/N 24-1, 24-103 through 24-2843, except 24-2563 ....91/96 min Octane 30 USG (Note 1 refers to including 2 gal as unusable fuel but only to the 4 tank airplanes, or those with optional 4 tank wings, as described by S/N)

PA-24-250 S/N 24-2563, 24-2844 through 24-3687 and PA-24-260: 91/96 octane min 28 USG (Note 1 aplies here, but the note ONLY applies to the calculated empty weight as 4 gal of fuel must be included in the empty weight of the aircraft, not included in the fuel capacity as described in the TCDS...text follows)

NOTE 1. Current weight and balance report including list of equipment included in certificated empty weight, and loading instructions when necessary, must be provided for each aircraft at the time of original certification. The certificated empty weight and the corresponding center of gravity location must include unusable fuel (not included in fuel capacity (by definition in this TCDS fuel capacity is the 30 or 28 gal stated in the Fuel Capacity line item for the -250/-260)) as follows: 24 lb. at (+90) for Model PA-24-250 S/N 24-2563, and 24-2844 through 24-3687; and for Model PA-24-260; and 36 lb. at (+90) for Model PA-24-400; S/N 26-2 through 26-148. (Blue underlined text is my comment)

The way I read this is that the 2 gal unusable is not actually there. The 28 gal stated capacity is the true capacity, all usable, but through some sleight of hand trick, Piper managed to not have to recertify the fuel system when changing its design by just adding in phantom weight for "unusable" fuel that was still in the fuel truck. I believe that the dog dish on the 260's does accurately reflect 28 gal in the mains, and most of the 4 tank aircraft that I have seen do reflect 30 gal as total wing tank capacity, however bogus that that is, but it does have merit based in the TCDS, but some are actually in compliance with CAR 3 in also stating 28 gal is the usable capacity.

This is my somewhat not terribly expert opinion based on fact and field experience, and how the FAA would look at this. Clear as MUD?

-Zach

[Ben Ayalon]