A short history of the subsystem that grounded the F-35

It has been described by Lockheed Martin as "revolutionary" and a "lofty technology challenge" so important that it was included in Secretary Robert Gates' tour of the F-35 assembly plant in September 2009 (see photo above).

The power and thermal management subsystem is called the Honeywell integrated power package (IPP), and it is currently the reason why no F-35s are flying.

We don't know how long the grounding order caused by an undisclosed IPP malfunction on 2 August will last. Since the announcement landed in our email inbox at 14:14 on 3 August, the programme has been in communications black-out mode. Even its normally chatty Twitter page has gone silent. That is not a good or a bad sign, although it is never re-assuring. It really means we still don't know anything about the incident or its consequences.

But we do know many things about the IPP. This relatively unknown subsystem is one of the few innovations -- along with the shaft-driven lift-fan, electro-hydrostatic actuators and engine-mounted starter/generator-- that distinguish the F-35 as a technological trailblazer. The F-35 is one of the first "more-electric aircraft", meaning it uses electricity to replace several functions formerly fueled by hydraulics or pneumatics. The IPP is the heart of the power and thermal management system. Its roughly 200hp gas turbine engine sends power to the starter/generator, which powers on the F-35's engine, which, in turn, powers up the generator. The IPP then manages the air-cycle cooling system, plus acts an emergency power supply in case both starter/generators happen to fail.


The IPP has been the focus of concerns throughout the development and flight test programme. Here's a brief catalogue of the major issues that have surfaced since the IPP started the first F-35 test engine six years ago.

• April 2005: IPP performs first engine start
• 21 Aug 2007: While operating in cooling bleed mode, the IPP shut down on the integrated test stand. The test stand was damaged as a result of the shut down and had to be refurbished, according to the Defense Contracts Management Agency (DCMA). An issue with a rotor was blamed for the shut down. "They believe that the rotor contacted the stator and gradually wore the stator, the rotor's sleeve and the enclosing magnet," DCMA reported.
• October 2007: DCMA reports IPP oil samples have unallowable traces of nickel alloy. "Stator and rotor clearance issues within the IPP have been identified as the root cause. Design clearance corrections are being implemented, and a rebuilt IPP is forecasted for availability in late October following successful acceptance testing."
• 17 October 2007: Honeywell delivered a redesigned IPP to Lockheed Martin
• March 2010: The Government Accountability Office (GAO) reports that exhaust from the engine and integrated power package exhaust may cause excessive damage to the flight deck environment and runway surfaces that may result in operating limits or drive costly upgrades and repairs of JSF basing options".