As an adaptation to rough-field operations, the main air inlet can be closed completely and the auxiliary air inlet on the upper fuselage can be used for takeoff, landing and low-altitude flying, preventing ingestion of ground debris. Thereby the engines receive air through louvers on the LERXs which open automatically when intakes are closed. However the latest variant of the family, the MiG-35, eliminated these dorsal louvers, and adopted the mesh screens design in the main intakes, similar to those fitted to the Su-27. The MiG-29 has a ferry range of 1,500 km without external fuel tanks, and 2,100 km with external tanks. The internal fuel capacity of the original MiG-29B is 4,365 litres distributed between six internal fuel tanks, four in the fuselage and one in each wing. For longer flights, this can be supplemented by a 1,500-litre (330 Imp gal, 395 US gal) centreline drop tank and, on later production batches, two 1,150-litre (253 Imp gal, 300 US gal) underwing drop tanks. In addition, a newer models have been fitted with port-side inflight refueling probes, allowing much longer flight times by using a probe-and-drogue system. The cockpit features a conventional centre stick and left hand throttle controls. The pilot sits in a Zvezda K-36DM ejection seat which has had impressive performance in emergency escapes. The cockpit has conventional dials, with a head-up display (HUD) and a Shchel-3UM helmet mounted display, but no HOTAS ("hands-on-throttle-and-stick") capability. Emphasis seems to have been placed on making the cockpit similar to the earlier MiG-23 and other Soviet aircraft for ease of conversion, rather than on ergonomics. Nonetheless, the MiG-29 does have substantially better visibility than most previous Russian jet fighters, thanks to a high-mounted bubble canopy. Upgraded models introduce "glass cockpits" with modern liquid-crystal (LCD) multi-function displays (MFDs) and true HOTAS. The baseline MiG-29B has a Phazotron RLPK-29 radar fire control system which includes the N019 "Sapfir 29" look-down/shoot-down coherent pulse-Doppler radar and the Ts100.02-02 digital computer. The N019 radar was not a new design, but rather a development of the Sapfir-23ML architecture used on the MiG-23ML.