British Airways Engineering,

> Aircraft Maintenance,
>
> 9^th^ Floor TBC, South Wing,
>
> Bay 4, (S469).
>
> PO Box 10,
>
> Heathrow Airport, Hounslow, Middlesex, TW6 2JA.

23^rd^ Jan 2008

REF--10067353-000-00

U.S. Department of Transportation,

Docket Operations,

M-30, West Building Ground Floor,

Room W12-140,

1200 New Jersey Avenue, SE.,

Washington, DC 20590.

**[SUBJECT:]{.underline}**

**Docket No. FAA-2007-03080; Directorate Identifier 2007-NM-160-AD**

British Airways (BA) has reviewed the FAA NPRM 2007-NM-160-AD, dtd Dec
11, 2007, and the applicable Service Bulletin (SB) 747-27A2398. BA
accepts the need to introduce the revised flap transmission attachment
design but offer the following comments:

**[1. Man Hours / Costs of Compliance]{.underline}**

BA heavy maintenance experience indicates it is not possible to do the
work content of the SB in the time stated in the original Boeing
publication. This has been discussed with Boeing, who concurred that an
estimation error had been made. The SB data states 109hrs per aircraft
and 52hrs for all component work (161hrs total). Subsequent Boeing
review recommended changing the aircraft man hour content to 258hrs per
aircraft whilst maintaining the existing component rework at 52hrs,
giving a total of 310hrs per aircraft. To date this revised man hour
data has not been published but it is twice as many man hours as stated
in the NPRM.

As the subsequent Boeing analysis is significantly different to the
content of the SB and the NPRM, BA requests the FAA to co-ordinate with
Boeing to correct the SB and NPRM published man hours and costs of
compliance.

**[2. Parts Installation (h)]{.underline}**

The Notice of Proposed Rulemaking, Parts Installation (h), prohibits the
use of pre-SB hinge braces and support assemblies (which is a sub-part
of the flap transmission) during the compliance period. Irrespective of
this prohibition,

SB 747-27A2398 introduces four key features (flap track machining, new
hinge brace, new support assembly, new bolts), which form a new assembly
configuration. BA believes this change makes the post-SB installation
significantly geometrically different, such that it mechanically
prevents the installation of the prohibited pre-SB parts (see SB
747-27A2398, Fig's 5 / 6 / 7 and 8, sht. 3 of 4, for the reversed hinge
brace and support assembly configuration).

However, BA's experience indicates there are events when hinge braces
and

flap transmissions may require disturbance or replacement other than
during

SB 747-27A2398 embodiment that would be affected by the proposal
restriction:

\- Fault Isolation Manual investigation of flap primary / flap drive
messages:

FIM 27-50-00-990-808-001, Fig 110, sht.6, Block 50 recommends replacing
the flap transmission (which incorporates support assemblies 65B8192-X
and 65B81950-X).

\- Flap transmission oil leakage repair (ref 747-SL-27-170):

Requiring flap transmission replacement (which incorporates support
assemblies 65B8192-X and 65B81950-X).

\- O/B Flap track moveable fairing removal / installation (ref AMM
27-51-31/401):

Flap track fairing installation requires a wear check of the hinge brace
and mount features per AMM 27-51-31/601 (such as refitting after
operating with the fairing removed per CDL Item No. 27-51-2).

\- Flap track clevis inspection (ref SB 747-57-2307):

Clevis inspection failure may result in removal of the flap transmission
(which incorporates support assemblies 65B8192-X and 65B81950-X) or
hinge brace.

\- MPD 57-600-00 / 57-620-00 flap track general visual inspection:

Inspection failure may result in removal of the flap transmission (which
incorporates support assemblies 65B8192-X and 65B81950-X) or hinge
brace.

\- MPD 57-866-01 / 57-946-01 / 57-876-01 / 57-954-01 TE flap zonal
inspections:

Inspection failure may result in removal of the flap transmission (which
incorporates support assemblies 65B8192-X and 65B81950-X) or hinge
brace.

Per the proposal, any of the above work for pre-SB aircraft would
require removed hinge braces and flap transmissions to be replaced with
post-SB parts. Yet the new parts will only mate with post-SB reworked
flap tracks. Consequently any disturbance of these parts would compel
operators to do SB 747-27A2398 on the flap assembly, forcing unscheduled
flap track rework or replacement (wherever the aircraft is and before
further flight). From BA's operational and minor maintenance experience,
the above work can and does result in unscheduled removal of hinge
braces and flap transmissions. The proposed parts prohibition is likely
to result in aircraft being grounded at locations not equipped to
support flap track rework and / or replacement.

BA believes the intent of the SB is for the rework to be carried out in
a controlled manner during scheduled heavy maintenance due to the
critical nature of the flap track rework, as well as the significant man
power to required to embody it. Hence, BA considers it essential to
allow continued use of pre-SB hinge braces and flap transmissions to
service aircraft with pre-SB flap tracks until their scheduled SB
maintenance input complete.

As SB 747-27A2398 introduces flap track oversize hole rework, new hinge
brace forging geometry, new support assembly forging geometry with
oversize mount holes and increased diameter mount bolts, BA believes it
is not possible to install pre-SB parts on post-SB modified flap tracks.
Therefore, BA requests the Parts Installation (h), is amended to allow
the continued use of pre-SB hinge braces and support assemblies on
pre-SB aircraft during the compliance period.

Mark Paine,

Senior Technical Engineer,

B747 Aircraft Systems.