ST Aerospace Mobile, Inc 

2100 9th Street, Brookley Complex 

Mobile, Alabama 36615, USA 

Tel : (251) 438 8888 

Fax : (251) 438 8892 

Singapore Technologies 

Engineering 

Page 1 of 4

FAA Atlanta 15th December, 2011 

Subject: Petition for Exemption 

Reference: FAA Project Number ST13005AT-T 

Dear Mr. Avella, 

ST Aerospace Mobile (STA Mobile) is the applicant for a multiple airplane Supplemental Type 

Certificate (STC) for conversion of Boeing 757-200 passenger airplanes into an “8 pallet/80-passenger” 

Combi configuration under FAA Project Number ST13005AT-T. STA Mobile expects issuance of STC by 

the end of 2011. 

STA Mobile respectfully submits this letter to petition for an exemption for § 25.783(c) and § 

25.783(d)(3)(i), to allow the current Main Deck Cargo Door (MDCD), part number 65-25326-90710 which 

was approved under STC ST03562AT for the STA Mobile 757-200SF conversion, to be used for the STA 

Mobile 757-200 Combi configuration. 

STA Mobile requests that the publication and comment procedures be waived in accordance with 

§ 11.29 and § 11.87 for the following reasons: 

i. The FAA had approved the MDCD for STC ST03562AT (STA Mobile 757-200SF) 

ii. The FAA clarified the requirements of § 25.783(c) and § 25.783(d)(3)(i) late in the STC 

certification program 

iii. This time-limited exemption is temporary, and STA Mobile must implement design changes 

to meet the requirements of § 25.783 Amendment 25-114. 

iv. Further delay of STC issuance would increase the harm to STA Mobile’s follow-on business 

and delay Combi conversions of airplane necessary to support NATO relief operations. 

DESCRIPTION OF CONVERSION 

The STA Mobile 757-200 Combi configuration is derived from the STA Mobile 757-200SF certified by 

STC ST03562AT. The combi modification is similar to that of the STA Mobile 757-200SF except that the 

forward main deck cabin aft of the Rigid Cargo Barrier (RCB) will be converted to a Class C Main Deck Cargo 

Compartment (MDCC) and the main deck cabin aft of Station 1119 approximate is retained with minor 
Singapore Technologies 

Engineering 

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modifications to accommodate 80 passengers and up to 3 flight attendants separated from the MDCC by a 

smoke barrier. The MDCD identical to the STA Mobile 757-200SF forms part of the MDCC. 

DESCRIPTION OF THE ISSUE

STA Mobile’s intention for project ST13005AT-T was to reuse the design of the MDCD that was 

approved in STC ST03562AT and in the Boeing 757-200 Special Freighter. This design has been 

evaluated and it meets and exceeds the requirements of § 25.783 Amendment 25-88. However, because 

§ 21.101 requires that a “changed product complies with the airworthiness requirements applicable to the 

category of the product in effect on the date of the application for the change”; the MDCD must now meet 

the requirements of § 25.783 Amendment 25-114. As explained below there are three requirements from 

Amendment 25-114 that the MDCD does not meet. Due to some confusion over the original approval 

basis, this issue was only raised by the FAA late in the program. Thus, STA Mobile had proceeded in 

good faith with the understanding that the existing MDCD design would meet the certification basis for 

this program. STA Mobile has already modified one airplane and having to make design changes at this 

time will further delay the delivery of the modified airplane and expose STA Mobile to a significant 

financial penalty. It is STA Mobile’s intention to make the appropriate design changes to the MDCD to 

ensure that it meets the requirements of § 25.783 Amendment 25-114 for which we are asking an 

exemption to. However, STA Mobile needs time to develop these design changes. 

STA Mobile determined that the MDCD does not meet these requirements from § 25.783 at 

Amendment 25-114: 

1. The MDCD has two vent pressure doors located on the lower half of the door and are hinged 

inward-opening. The vent pressure doors are open until the latches are fully closed. The 

hinge fittings of each pressure door have stop locks, which engage the latches to preclude 

closure of the pressure doors until all four pairs of latches are in fully latched position. 

Conversely, the latches cannot be rotated to the open position until the pressure doors are 

open. If they are not latched, the pressure doors cannot close. This will prevent 

pressurization of the airplane to an unsafe level if the MDCD is not fully closed, latched, and 

locked. However, the pressure doors can close as soon as the latches are in their fully 

latched position. They do not monitor the latch and lock condition as required by § 25.783(c). 
Singapore Technologies 

Engineering 

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2. There is one latch lock per pair of latch on the MDCD, and not an individual lock for each 

latch as required by § 25.783(d)(3)(i). 

3. The MDCD has view ports which only show that the MDCD is latched and do not provide an 

adequate view of the locks. The MDCD does not meet the requirements of § 25.783(f). This 

requirement is not part of the exemption request. ST Aerospace will be requesting an 

exception to this requirement per CFR 21.101. 

There are 79 757-200 Production Freighters, 34 757-200 Special Freighters and 1 Combi 

Freighter produced by Boeing, that have the identical MDCD installed. As of today, these aircraft have 

accumulated more than 2,740,360 flight hours and 1,885,412 flight cycles without any significant service 

difficulties. Service history information is attached separately. 

To date, STA Mobile has re-delivered forty-seven (47) STA Mobile 757-200SF configured 

airplanes since the issuance of STC ST03562AT on April 2, 2008 and the MDCD has accumulated a 

considerable satisfactory service history. 

EVALUATION OF PUBLIC INTEREST: 

Granting this petition is in the public interest because: 

• It allows adequate time for STA Mobile and its supplier to develop an effective design 

solution to ensure that the new design meets the latest Amendment level. STA Mobile 

needs the time to ensure that the new design is robust and that it will not introduce 

unintended consequences. 

• It will also allow the modified airplane to return to service. The airplane will be used in 

support of NATO operations starting in January 2012. 

• It will raise the safety level of the airline fleet because airlines will have to replace the 

Boeing 757-200s that are modified to Combis with new airplanes that meet newer 14 

CFR Part 25 Amendments. 

• It will help in the reduction of air pollution because Combi-configured airplanes will 

optimize the space usage in flights in cases where there is a low demand in passenger 

flights and a high demand in cargo transportation thus reducing the number of flights.