Apple is poised to introduce new versions of its Time Capsule wireless backup appliance and AirPort Extreme 802.11n wireless routers, regulatory filings with the Federal Communications Commission reveal.

A filing for a new AirPort Express (ID Label diagram) was originally lodged in January and granted on Monday, while a filing for a new Time Capsule (ID Label diagram) was first made back in August of 2008 and also granted this week.

The documents appear to indicate that Apple is adding a combined mode, allowing its AirPort base stations to simultaneously support iPhones and other 802.11b/g devices operating at 2.4 GHz, while also broadcasting 802.11n wide signals in the 5GHz band to maximize throughput for notebooks and devices such as Apple TV. Existing models can only run in one mode or the other, providing either wide compatibility or the highest possible network performance, but not both.

As noted in our original review of Time Capsule, there is also significant room for improvement in the performance of its embedded file server, although the FCC documents only refer to the devices' radio features. There is no mention of adding femtocell 3G support to the AirPort products, for example.

The filings come two weeks after AppleInsider relayed a report from Australia's whirlpool forums which recommended that Australian Mac users not purchase any of the company's existing AirPort products because a source was informed by his employer that "there will be new Airport Extreme and Airport Express within the next few weeks."

While Apple has reflected relatively healthy inventory of AirPort Extremes in the US and Canada, availability of the wireless routers has been close to non-existant for the past 2-3 weeks in parts of Europe, such as Sweden, Norway, Denmark, France, Germany, and Italy.

An AppleInsider blog post published earlier today noted rumors of six new Apple product part numbers that have turned up in the inventory systems of some of the company's overseas resellers. Typically when the FCC publishes authorization documentation for a new Apple product, that product hits the market within days of the grant being made public.

It should also be noted that Amazon recently slashed the price of the current generation Time Capsules by 13 - 22 percent, a move which may now be seen as an inventory clearing measure ahead of new models. The 1TB Time Capsule was marked down $112 to $387.92 while the 500GB model was reduced by about $40 to $259.31.

More FCC documents

AirPort Extreme: Authorization Letter [PDF], Request for confidentiality [PDF], and Test report [PDF]