The Australian Transport Safety Bureau recommends that the
Federal Aviation Administration (Piston Engine Certification
Directorate) review the certification requirements of piston
engines with respect to the operating conditions under which
combustion chamber deposits that may cause preignition are
formed.
The Office of Accident Investigation is in receipt of your
recommendations regarding "PA-31-350 Engine Failure."
Your recommendations have been forwarded to the appropriate office
for response, which is normally 90 days. Your recommendations have
been identified as 02.141 and 02.142 and inquiries should reference
these numbers.
You will be kept informed as to the progress and final resolution
of your submission. If you have any questions or need additional
information regarding these safety recommendations, please notify
[Name Supplied], AAI-210, at [Telephone Number Supplied].
Thank you for your letter of 5 August 2002 advising the outcome
of considerations by your Safety Recommendations Review Board to
FAA Safety Recommendations 02.141 and 02.142. These recommendations
(R20010254 and R20010255 respectively) were issued by the
Australian Transport Safety Bureau in December 2001 following its
investigation into the accident involving Whyalla Airlines Piper
Chieftain VH-MZK in Spencer Gulf, South Australia on 31 May 2000,
in which there were eight fatalities.
The ATSB appreciates the consideration that the FAA has given the
recommendations and investigation report. A great deal of work and
thought went into the engine failure analysis, but it was beyond
the resources of the ATSB to delve too much further into the issues
that we have raised. In this regard, we were pleased to learn that
the FAA considered that further evaluation of the issues we had
identified was justified. We are in the process of preparing a case
study that will include detailed information on 10 other failures
of high-powered reciprocating engines that we have investigated. We
will forward a copy of that document to you upon its release, as it
may assist your ongoing testing and other activities in this
area.
The ATSB is greatly interested in the outcome of the work you will
be undertaking with respect to the two recommendations. We would
appreciate any advice you are able to provide, such as progress
reports or other information as it becomes available.
This recommendation referred to the certification requirements of piston engines with respect to operating conditions under which combustion chamber deposits that can cause preignition are formed.
Preignition, like detonation, is a form of uncontrolled combustion that occurs in piston engine cylinders. The symptoms and consequences of both these events are very similar, differing only in the sequence of occurrence. Preignition occurs before scheduled ignition, and detonation occurs after ignition. Current FAA certification requirements and guidance provide for margin against detonation. The current FAA certification regulation that addresses piston engine detonation is (Regulations)33.47. FAA guidance describing acceptable methods of compliance with this regulation is contained in Advisory Circular (AC) 33.47-1. To meet these acceptable methods, the applicant must test the engine at worst-case conditions for detonation, which are also the most critical conditions for preignition. Instrumentation used to monitor for detonation, such as pressure sensors or pieziolectric vibration sensors, will identify all types of uncontrolled combustion, including both detonation and preignition. To pass the test, the applicant must substantiate that a 12% margin exists between the leanest fuel mixture and the onset of uncontrolled combustion. This margin is intended to accommodate the deteriorating resistance of the engine to detonation and preignition as it ages and accumulates combustion chamber deposits during the overhaul interval. The FAA is currently conducting an extensive evaluation of the detonation characteristics of high performance reciprocating engines at the FAA Technical Centre. The relationship between deposit formation and octane rating increase of the engine will be investigated. Data from this evaluation will be used to assess the adequacy of the current regulation and advisory material. Service experience with certificated reciprocating engines will also be monitored for detonation incidents and appropriate corrective action will be taken if a service problem is revealed
I refer to two safety recommendations that the ATSB issued to the FAA in December 2001 that arose from the ATSB's investigation into the Whyalla Airlines PA3l-350 accident that occurred on 31 May 2000.
In your letter of 5 August 2002, you advised that an FAA Safety Recommendations Review Board had classified responses to recommendations 02.141 and 02.142 as "Closed -Acceptable Action". The memorandum attached to your letter outlined the action that the Aircraft Certification Service, Engine and Propeller Directorate intended to take concerning the recommendations. As it is now over 12 months since receiving your correspondence, I wanted to check with you regarding the progress the FAA has made in examining those issues.
Further, our investigation into the engine malfunctions in the accident aircraft, as well as engines that had malfunctioned in other aircraft, revealed clear evidence of corrosion damage to the aluminium alloy layer in the bearings where the alloy was exposed at the bearing insert ends. The ATSB's report on the accident stated that the formation of lead oxy bromides instead of lead bromide would affect the quantity of free bromine remaining after the scavenge process. Excess bromine can find its way into the lubricating oil and form hydrobromic acid. The ATSB would also be interested in any observations or data the FAA might have gained regarding excess bromine from the evaluation of piston engine performance characteristics it was conducting.
ATSB Comment
Subsequent to the ATSB response of 9 October 2003, the ATSB has released a research report into aircraft reciprocating-engine failures, B2007/0191.
The ATSB now closes this recommendation.
