An aircraft (20, 200) comprising: a fuselage (22, 222); a first passenger cabin (32, 204, 304, 404, 504, 604, 704, 804) having a first floor (38, 207); a split level cabin located in the fuselage (22, 222) forward of the first passenger cabin (32, 204, 304, 404, 504, 604, 704, 804), the split level cabin including an upper second cabin (34, 206, 306, 406, 506, 606, 706, 806) having a second floor (40, 208) above a level of the first floor (38, 207), and a lower third cabin (36, 210, 310, 410, 510, 610, 710, 810) beneath the upper second cabin (34, 206, 306, 406, 506, 606, 706, 806) and having a third floor (42, 212) below the level of the first floor (38, 207), the second cabin comprising a first structure (224, 324, 424, 524, 624, 724, 824) at an interface between the upper second cabin and the first cabin configured to permit traversal between the second cabin and the first cabin and the third cabin comprising a second structure (221, 321, 421, 521, 621, 721, 821) at an interface between the lower third cabin and the first cabin configured to permit traversal between the third cabin and the first cabin; and a lower hold compartment (46, 214) located beneath at least a portion of the lower third cabin (36, 210, 310, 410, 510, 610, 710, 810), wherein a first portion of the fuselage (22, 222) is substantially adjacent to the second upper and third lower cabins (34, 36, 206, 210, 306, 310, 406, 410, 506, 510, 606, 610, 706, 710, 806, 810) and has a substantially first cross sectional shape along a length of the first portion, wherein a second portion of the fuselage (22, 222) is substantially adjacent to the first passenger cabin (32, 204, 304, 404, 504, 604, 704, 804) and has a substantially second cross sectional shape along a length of the second portion, wherein the first cross sectional shape has a lowered keel line relative to the second cross sectional shape, wherein an aft portion of the lowered keel line of the first portion of the fuselage (22, 222) is aerodynamically faired into an adjacent region of a wing-to-body fairing with a keel line that is no higher than the lowered keel line of the first portion of the fuselage (22, 222), wherein the aircraft further comprises a crushable zone (60, 260) within the fuselage (22, 222) beneath the lower third cabin (36, 210, 310, 410, 510, 610, 710, 810) for absorbing energy of an impact of the fuselage (22, 222) during a crash landing, and wherein the fuselage (22, 222) further comprises a keel (185, 220) and the crushable zone (60, 260) comprises at least 76,2 cm of vertical height between the third floor (42, 212) and the keel (185, 220) including the lower hold compartment (46, 214). a fuselage (22, 222); a first passenger cabin (32, 204, 304, 404, 504, 604, 704, 804) having a first floor (38, 207); a split level cabin located in the fuselage (22, 222) forward of the first passenger cabin (32, 204, 304, 404, 504, 604, 704, 804), the split level cabin including an upper second cabin (34, 206, 306, 406, 506, 606, 706, 806) having a second floor (40, 208) above a level of the first floor (38, 207), and a lower third cabin (36, 210, 310, 410, 510, 610, 710, 810) beneath the upper second cabin (34, 206, 306, 406, 506, 606, 706, 806) and having a third floor (42, 212) below the level of the first floor (38, 207), the second cabin comprising a first structure (224, 324, 424, 524, 624, 724, 824) at an interface between the upper second cabin and the first cabin configured to permit traversal between the second cabin and the first cabin and the third cabin comprising a second structure (221, 321, 421, 521, 621, 721, 821) at an interface between the lower third cabin and the first cabin configured to permit traversal between the third cabin and the first cabin; and a lower hold compartment (46, 214) located beneath at least a portion of the lower third cabin (36, 210, 310, 410, 510, 610, 710, 810),