Guidance is by inertial navigation until the missile is close enough to the target to use active radar for terminal homing. The K-100 has an enlarged () derivative of the Agat 9B-1103M seeker used in the R-27 (air-to-air missile) (AA-10 'Alamo'). It has a lock-on range of , described by an Agat designer as "one fifth or less of the overall range". Variant KS-172 Prototype in 1993. KS-172S-1 Prototype in 2003. Similar weapons R-37 (missile) (AA-X-13/AA-13 'Arrow') was developed from the R-33 (missile) (AA-9 'Amos') and is intended for the Sukhoi Su-35 Flanker-E, Sukhoi Su-37 Flanker-F, MiG 1.42 MFI and other future fighters. According to Defence Today the range depends on the flight profile, from for a direct shot to for a cruise glide profile. Jane's reports two variants, the R-37 and the R-37M; the latter has a jettisonable rocket booster that increases the range to "300-400km" (160–220nmi). Work on the missile appears to have restarted in late 2006, as part of the MiG-31BM programme to update the Foxhound with a new radar and ground attack capability. Kh-31 (AS-17 'Krypton') – the Chinese have licensed the anti-radar version (Kh-31P) of this Russian air-to-surface missile, and may be working on an "AWACS killer" variant of their YJ-91 derivative. The Russians claim the anti-shipping version, the Kh-31A, can be adapted for use as an AWACS killer. AIM-54 Phoenix – Now retired, a -range missile that was carried by the US Navy's F-14 Tomcat. AIM-97 Seekbat - based on the Standard Missile SAM, the Seekbat was an extremely long-ranged missile designed to shoot down the MiG-25 Foxbat, which at the time had almost mythical performance estimates. When the real-world performance of the Foxbat was found to be dramatically less impressive, development was cancelled. See also AIM-152 AAAM FMRAAM Meteor (missile) R-37 (missile) PL-21 References External links sukhoi.ru – unofficial site with photos from MAKS air show; photos 10,12 and 13 show the K-100 on the ground of which maks2007d1013.jpg is perhaps the best. Weapons of Russia Air-to-air missiles of India Air-to-air missiles of Russia NPO Novator products Military equipment introduced in the 2000s