On March 4, 2011, about 0400 central standard time, a Learjet 25D, XA-TWH, was substantially damaged when it impacted obstructions while landing at William P. Hobby Airport (HOU), Houston, Texas. The two pilots, two medical crewmembers, and two passengers were not injured. The airplane was registered to Grupo Desarrollador Mares del Pacifico, S.A. de C.V., and operated by Personas y Paquetes Por Aire, S.A. de C.V. under the provisions of 14 Code of Federal Regulations Part 129 as a foreign air carrier air ambulance flight. Night instrument meteorological conditions prevailed and an instrument flight rules flight plan was filed. The flight originated about 0140 from Angel Albino Corzo International Airport (MMTG) Tuxtla Gutiérrez, Chiapas, México. During the landing on runway 12R, the airplane exited the southeast end of the runway, struck, and damaged the instrument landing system (ILS) localizer antenna system. The airplane continued traveling about 1,000 feet past the end of the runway and came to rest upright in a flat grassy area. The pilot and the co-pilot both stated that due to the fog and low visibility they could not see the far end of the runway and flared the airplane too high. After landing long on the runway the pilot said he applied maximum braking and reverse thrust but could not stop the airplane before colliding with the ILS antenna system. The operator reported that there was no mechanical malfunction or failure. The operator stated that the decision not to delay the flight and to land in marginal conditions was influenced by medical considerations for the passenger, who needed immediate specialized medical treatment. A review of recorded data from the HOU automated weather observation station, revealed the conditions at 0353 were wind from 200 degrees at 3 knots, visibility of 3/4 mile in mist, an indefinite ceiling at 200 feet, temperature of 19 degrees Celsius (C) , dew point of 18 degrees C, and an altimeter setting of 29.90 inches of Mercury.