Graham Warwick/WASHINGTON DC

The USAF is pushing its bombers to the forefront of the expeditionary air force concept. But how long can they last?

Deployment side by side of Northrop Grumman B-2s and Boeing B-52s is set to become commonplace as the US Air Force seeks to integrate the former into its long-range bomber force.

Operation of the B-2A stealth bomber, alongside the B-52H and the Rockwell B-1B, is central to the USAF's force projection plans for the next four decades - the time it will take to develop and field a replacement global attack capability.

The USAF briefed the US Congress in early March that it will not need to replace the "large payload, long range and rapid-response characteristics inherent in our bomber force" before 2037 - provided that it is able to sustain the current aircraft with upgrades to improve maintainability, deployability and survivability.

The USAF is seeking funds for almost $2.3 billion in improvements to add to the $3.6 billion already being spent to upgrade the capability, reliability and maintainability of its bombers (Flight International, 17-23 March).

The bomber roadmap briefed to Congress is based on sustaining a force of 130 combat-coded aircraft. According to USAF forecasts of attrition rates and service lives, the present force will fall below the 170 aircraft needed to sustain 130 combat-coded bombers by 2037. The service is therefore projecting that it needs to begin production of a replacement "global attack platform" by 2034, to achieve initial operational capability by 2037.

The USAF has been careful not to limit itself to replacing its bombers with another bomber - it talks about a capability, not an aircraft, when discussing the eventual successor to its B-1s, B-2s and B-52s. "We say 'capability' rather than 'bomber' since technological advances may lead us to a configuration or platform that in no way resembles today's bomber aircraft," it says.

Studies are under way to identify the enabling technologies for the "next-generation global attack capability", and are looking at manned aircraft, unmanned air vehicles, missiles and even space-based systems as potential successors to today's bombers.

For the next four decades, however, the B-1, B-2 and B-52 will form the backbone of the Aerospace Expeditionary Forces (AEFs) - quick-response forces being developed to replace the USAF's declining permanent overseas presence. As part of an AEF, long-range bombers will be able to be launched from the continental USA within hours, to forward deploy or to strike targets. The USAF argues that the bombers' long range and large payload give flexibility. Aircraft can be deployed on alert at forward operating locations to act as a deterrent, as with the Kosovo crisis, or they can be used to strike rapidly from the USA and conduct follow-on operations from the forward operating location. Alternatively, they can strike and return to the USA.

Maintaining that flexibility for another 40 years will require investment, the USAF argues, and its bomber roadmap details the upgrades that the service considers necessary to keep the current force viable. Broadly, these upgrades break down into those desired to improve crew situational awareness and aircraft survivability, and those required to combat obsolescence and to sustain capability.

The USAF has divided its upgrade plans into near term (2000-10), mid-term (2006-15) and long term (2015 onwards). Needed near-term upgrades are:

· Link 16 line-of-sight datalink for the B-1 and B-2, to provide connectivity and improve situational awareness and survivability. The B-1 would also receive a beyond-line-of-sight datalink capability;

· EHF satellite communications for the B-2, to provide secure command and control of the USA's nuclear forces;

· improvement of the B-52's electronic countermeasures system to replace unreliable and unsupportable equipment and improve situational awareness.

These total $891 million, of which around $30 million has been funded so far. The USAF's desired mid-term upgrades, none yet funded, total $678 million and include:

· a B-1 cockpit upgrade providing a graphics display capability to improve situational awareness and survivability, with common displays in the front and rear crew stations;

· Link 16 datalink for the B-52, plus a 1760 weapons databus interface in the bomb bay to allow the internal carriage of smart munitions. The B-52 can carry such weapons only on external pylons;

· digital engine controllers for the General Electric F118-powered B-2, to replace the current high-failure analogue controllers. Without these, the USAF says, it will be forced to ground aircraft beginning in 2008.

These upgrades would sustain the bomber force to 2015. To go beyond that, and to keep the current aircraft in service for another 35 years as planned, the USAF has identified candidate long-term upgrades. These include:

· a B-1 radar upgrade to increase synthetic-aperture radar resolution from 3m to 0.3m or better, enabling the aircraft to find and engage targets autonomously and precisely with direct attack or stand-off munitions;

· reduction of the B-2's low-observable signature to counter future threats, and replacement of the aircraft's computers to improve supportability and capability;

· an inflight attack planner/autorouter for the B-52, to allow updating or replanning of missions while en route to the target.

The long-term upgrades are budgeted at $685 million, which takes the total funding required to almost $2.3 billion. The B-2 would receive the most money, with $844 million to be spent on upgrading the stealth bomber, compared with $763 million for the B-52 and $679 million for the B-1. Despite planning these upgrades, the USAF is still coming to terms with the reality of a finite bomber force. The B-52 and B-1 are long out of production, and only 21 B-2s are being fielded. Therefore replacement plans are based on the expected useful lives of its existing aircraft. Its projections are based on a current force of 190 bombers: 93 B-1s, 76 B-52s and the 21 B-2s.

Surprisingly, it is not the B-52 which will determine when the bomber force drops below the minimum requirement of 170 aircraft. The B-52's service life is determined by the wing upper surface, which has an economic limit of 32,500-37,500h. Most airframes have logged fewer than 15,000h, and the USAF projects that the B-52 fleet will not fall below the minimum 62 aircraft required until 2044 - 84 years after the bomber first entered service.

The B-2 airframe is expected to last for around 40,000h, based on current mission profiles. The first structure to fail is predicted to be the drag-rudder attachment points, followed by the area around the aft deck that is subjected to high vibro-acoustic stress. Despite its relatively long airframe life, the small B-2 fleet is projected to drop below the minimum 19 aircraft required by 2027, because of attrition.

The B-1 poses the biggest problem in sustaining the US bomber fleet. Because of its high-speed, low-altitude mission profile, the swept-wing B-1 has the least life remaining - based on the point at which it becomes more economical to replace it than continue repairs. The economic service life is limited by the wing lower surface to 15,200h, and the USAF projects that the B-1 inventory will drop below the minimum requirement of 89 aircraft in 2018, based on current usage and mishap rates.

Long-range bombers remain central to the US Air Force's long-term planning and, while re-assuring Congress that the current aircraft can continue to do the job, its roadmap makes clear that, without the required upgrades, the expensive task of developing a new global attack capability will come sooner, rather than later.

Source: Flight International